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A LABORATORY MANUAL

FOR

COMPARATIVE VERTEBRATE ANATOMY

By Frank Logiudice

Department of Biology

University of Central Florida

© 2008 Frank Logiudice

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This book is dedicated to Orville M. Berringer, a fellow faculty member and a good friend. I

learned many of the dissection techniques utilized in this manual while teaching “Human

Anatomy” with him. Budd Berringer was a dedicated mentor to both students and fellow

faculty. He was a strong advocate for the University of Central Florida’s prehealth professional

students. Its was due to his efforts that the University of Central Florida Prehealth Professional

Office was established. His hard work and dedication helped many UCF students to enter into

careers in medicine, dentistry, and veterinary medicine and his instruction gave them the tools to

succeed in professional school. I have had the honor of teaching with many spectacular faculty

but Budd will always stand out in my mind as the one who had a profound influence in how I

approach the teaching of anatomy.

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TABLE OF CONTENTS

Introduction page 3

Chapter 1: Skeletal Structure page 8

Part A: Introduction page 8

Part B: The Axial Skeleton page 14

Topic B1: The Vertebrae page 14

Topic B2: The Ribs and Sternum page 23

Topic B3: The Skull page 23

Part C: The Appendicular Skeleton page 49

Topic C1: The Pectoral Girdle and Appendage page 49

Topic C2: The Pelvic Girdle and Appendage page 55

Chapter 2: Myology page 62

Part A: An Introduction page 62

Part B: Muscle Dissection Techniques page 65

Part C: The Muscles page 71

Topic C1: The Muscles of Squalus page 71

Topic C2: The Muscles of Necturus page 76

Topic C3: The Muscles of Felis page 83

Chapter 3: Visceral Organs and Angiology page 104

Part A: The Exposing the Visceral Organs and Angiology page 104

Topic A1: The Exposing the Visceral Organs and Angiology in Squalus page 104

Topic A2: The Exposing the Visceral Organs and Angiology in Necturus page 105

Topic A1: The Exposing the Visceral Organs and Angiology in Felis page 105

Part B: The Respiratory System page 106

Topic B1: The Respiratory System in Squalus page 106

Topic B2: The Respiratory System in Necturus page 108

Topic B3: The Respiratory System in Felis page 109

Part C: The Digestive System page 111

Topic C1: The Digestive System in Squalus page 112

Topic C2: The Digestive System in Necturus page 115

Topic C3: The Digestive System in Felis page 117

Part D: The Urogenital System page 122

Topic D1: The Urogenital System in Squalus page 122

Topic D2: The Urogenital System in Necturus page 126

Topic D3: The Urogenital System in Felis page 128

Part E: The Circulatory System page 135

Topic E1: The Circulatory System in Squalus page 135

Topic E2: The Circulatory System in Necturus page 150

Topic E3: The Circulatory System in Felis page 162

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Introduction

Comparative vertebrate anatomy is a study of the vertebrate form from both an

anatomical point of view and from an evolutionary perspective. It is a study of vertebrate

morphology and of the evolutionary changes that have occurred in the vertebrate body over time.

These changes caused the formation of new species that were able to exploit an increasing range

of resources and ecological niches. Today vertebrates are an extremely successful subphylum of

animals.

One important aspect of studying comparative anatomy is dissection. Dissection will

allow us to have direct observation of anatomy and should give us an appreciation of

evolutionary developments.

We will be using primarily three species over the semester in our study of comparative

vertebrate anatomy. They are the spiny dogfish (Squalus sukleyi or Squalus acanthias), the

common mudpuppy (Necturus maculosus), and the common house cat (Felis catus). These three

species are very useful for observing a number of vertebrate anatomical features and

evolutionary developments. In particular they will allow us to see the various anatomical

modifications that occurred as vertebrates evolved for a terrestrial existence.

Kingdom: Animalia

Phylum: Chordata

Subphylum: Vertebrata

Class: Chondrichthyes

Order Squaliformes

Family: Squalidae

Genus: Squalus

Squalus acanthias and Squalus sukleyi are two very similar species commonly called

“spiny dogfish”. These are small sharks that are considered to be relatively abundant (although

like most shark species their numbers have dropped off markedly in recent years). S. acanthias

is found in the Northern Atlantic while S. sukleyi is located in the Northern Pacific. Both species

can form large schools that tend to segregate by size and gender. They are active predators and

feed on a variety of small fishes and cephalopods. Females tend to be larger than males with

adult males ranging from 60-90cm (24-35 inches) and adult females from 76-107 cm (30-42

inches) in length. Squalus are long living fish reaching an age comparable to that of humans.

Females reach maturity at 12 years and have a gestation period of two years. They give birth to

live young (about five to seven pups per litter).

Squalus is very useful in comparative vertebrate anatomy because they demonstrate what

may be considered to be basal vertebrate anatomy. These are the earliest living representatives

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of the gnathostomata, the jawed vertebrates. Squalus and all sharks belong to the class

Chondrichthyes meaning that their skeleton is composed of cartilage. This is considered to be

the primitive vertebrate condition. Other vertebrates do retain some cartilage in the adult skeleton

but the bulk of the skeleton will be composed of bone. Also, the embryonic skeleton of

vertebrates will be composed of cartilage so Squalus is also useful from a developmental point of

view.

Kingdom: Animalia

Phylum: Chordata

Subphylum: Vertebrata

Class: Lissamphibia

Order Caudata

Family: Proteidae

Genus: Necturus

Necturus maculosus is a salamander species found in freshwater ponds, lakes, streams,

and rivers of eastern North America. They are nocturnal and purely aquatic. Necturus are

neotenic meaning that they are considered to be in a permanent larval state. They retain gills in

the adult state, which is reached in five or six years. This species can live to thirty years of age

or older. Necturus is a predator of small aquatic animals, in particular minnows and crayfish. N.

maculosus is the largest Necturus species and reaches a maximum length of 49 cm (19 inches).

Necturus maculosus is a nice example of the vertebrate transition between aquatic and

terrestrial existence. Although purely aquatic, these salamanders display tetrapod developments.

They have well-developed limbs with the standard tetrapod skeletal structures. However, like

fishes, it is the axial musculature that provides the main force for locomotion in these animals.

As a result, the axial musculature maintains a prominent segmental pattern as seen in fishes.

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Kingdom: Animalia

Phylum: Chordata

Subphylum: Vertebrata

Class: Mammalia

Order Carnivora

Family: Felidae

Genus: Felis

Felis catus is a species that is well known to most students. The common housecat has

been a companion of humans for thousands of years. They are intelligent mammals with a social

structure. Felis is also an efficient predator of small animals. This may have been one reason

behind its domestication and has also led to a loss of many species of birds and small mammals

in areas in which cats have been introduced.

As a mammal it displays all of the features of a vertebrate that has evolved for terrestrial

existence. Like Necturus it has limbs but these have been modified over those of the mudpuppy

and most of the locomotory force comes from the appendages. The skeleton has an increase in

differentiation and muscle attachment points. The appendicular muscles are greater in size,

number, and complexity of action. Felis is also an endotherm and an amniote. As a result we

will be able to observe specializations that are the result of endothermy and structural features

found in amniotes that are not found in other vertebrates.

_____________________________________________________________________________

Before you enter into the lab you should take some time to become familiar with basic

anatomical terminology. This will make it much easier for you to assimilate the information

presented to you in your first, and subsequent, lab sessions. You also would do well to study the

lab material prior to each lab session. Due to security concerns, equipment costs, and other

logistical concerns you most likely will not have access to the laboratory any time other than

your assigned laboratory section. You will want to maximize that lab experience by working

with the actual anatomical specimens and not waste it reading your book. You can read your

book anywhere but you will only have a short period of time each week to interact with the lab

specimens. No matter how well depicted, no illustration equals working with the real thing.

To start you off this chapter will introduce you to some of the terminology of anatomy.

You will find that a familiarity with these terms will make your first task of learning osteological

features to be much easier.

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1. Planes and Sections of the Body

To aid in the complex study of anatomy, it is often beneficial to divide into sections

through the use of planes (although this can also be done with surgical techniques as well).

(1) Sagittal Plane - a sagittal plane divides the body into right and left portions. If the

plane runs directly along the midline of the body it is termed a midsagittal plane. A

midsagittal plane will divide the body into equal right and left portions. If the plane

is off the midline it is said to be a parasagittal plane. A parasagittal plane will divide

the body into unequal right and left portions, the level of disparity depends on where

the plane is located.

(2) Frontal Plane (also termed Coronal) - a frontal plane divides the body into an anterior

and a posterior portion.

(3) Transverse Plane (also termed Horizontal or Cross Sectional) - a transverse plane

divides the body into upper (superior) a lower (inferior) portions.

2. Directional Terminology

!!!!!!!!!!! Directional terminology will also be invaluable to you in your studies.! You will notice

directional terms being used quite a bit in the naming of anatomical structures beginning with

osteological features.! One study method that may speed up your learning of these terms is to

consider them in opposite pairs (ex: superior vs. inferior).

!!!!!!!!!!! In directional terminology we are referring to the structure’s position in a body in the

anatomical position and relative to another structure.

!!!!!!!!!!! (1) Superior - to be above another structure. (Ex; the head is superior to the neck.)

!!!!!!!!!!! (2) Inferior - to be below another structure. (Ex; the neck is inferior to the head.)

(3) Anterior - to be in front of another structure. (Ex; the incisors are anterior to

the canines.)

!!!!!!!!!!! (4) Posterior - to be behind another structure. (Ex; the canines are posterior to the !!!!!!!!!!!

incisors.)

(5) Medial - to be along the midline axis of the body.! (Ex; the nose is medial relative to

the eyes.)

(6) Lateral - to be away from the midline of the body. (Ex; the eyes are lateral relative to

the nose.)

(7) Proximal - to be closer to the main axis of the body.! (Ex; the shoulder is proximal

relative to the wrist.)

(8) Distal - to be at a distance from, to be further from, the main axis of the body.! (Ex;

the wrist is distal relative to the shoulder.)

(9) Intermediate - to be between two structures, either between distal and proximal

structures or between lateral and medial structures.! The term “middle” can be used

for intermediate but middle and medial are not equivalent terms.! (Ex; your finger has

three bones called “phalanx” bones.! The one closest to your knuckle is the proximal

phalanx.! The one that your fingernail is on is the distal phalanx.! The one between is

intermediate, or middle, phalanx.)

(10) Deep - to be further from the surface of the body than is another structure, to be

beneath another structure.! (ex; the ribs are deep to the pectoralis major.)

(11) Superficial - to be closer to the surface of the body than is another structure.! (Ex;

the pectoralis major is superficial to the ribs.)

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!!!!!!!!!!! (12) Cranial/Cephalad - to mean specifically “towards the head”.

!!!!!!!!!!! (13) Caudal - to mean specifically “towards the tail”.

Squalus Skeleton Demonstrating The Differences Between the Axial and Appendicular Skeleton

Axial:

Chondrocranium

Splanchnocranium

Ribs

Vertebral

Column

Pectoral

Girdle &

Fins

Appendicular:

Pelvic

Girdle &

Fins

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Chapter 1: Skeletal Structure

Part A: An Introduction

The skeleton is the basic framework of the vertebrate body. It is the scaffolding on which

the muscles attach and which serves to protect the visceral organs. During the development, the

skeleton sets the pathway by which blood vessels and nerves grow. It is typically composed of

bone and cartilage.

The skeleton can be subdivided into the axial skeleton and the appendicular skeleton.

The axial skeleton is composed of the skeletal structures of the main axis of the body. These are

the skull, vertebral column, and rib cage. The appendicular skeleton is composed of the skeletal

elements of the limbs and their associated girdles.

Axial: Vertebral Column Ribs Splanchnocranium Neurocranium

Appendicular: Pelvic Girdle & Limbs Pectoral Girdle & Limbs

Necturus Skeleton Demonstrating The Differences Between the Axial and Appendicular Skeleton

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Cat Skeleton Demonstrating The Differences Between the Axial and Appendicular Skeleton

In extant agnathans and chondrichthyes the skeleton is composed exclusively of cartilage

(with the exception of the teeth in chondrichthyans). There are four classes of cartilage: hyaline

cartilage, fibrocartilage, elastic cartilage, and calcified cartilage. The skeleton of Squalus is

composed primarily of hyaline cartilage. The jaws are composed of calcified cartilage (also

known as mineralized cartilage). Calcified cartilage is cartilage that has become more rigid due

to an invasion of calcium salts into the cartilage matrix. This adds strength to the tissue, which is

beneficial in shark jaws.

The cartilage organ is composed primarily of cartilage tissue. However it is a true organ

because it is composed of more than one type of tissue. A membrane termed the perichondrium

surrounds it. The perichondrium is a connective tissue having two layers. The outer layer is a

tough fibrous connective tissue that allows the organ to withstand mechanical forces (much like

an athletic bandage strengthening an ankle). The inner layer a single layer of multipotent cells

that can produce new cartilage cells and repair the cartilage organ.

In other vertebrates the embryonic skeleton is initially composed of cartilage. During

development the cartilage is replace by bone to varying degrees. In Neopterygians there is a

significant amount of cartilage in the adult skeleton while teleosts have a highly ossified

skeleton. The adult skeletons of Necturus and Felis are composed mostly of bone but some

cartilage remains.

Osteology is the study of bone and the skeleton. Bone organs are true organs being

composed of several tissues working together to perform a task. Bone organs typically contain

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two classes of bone tissue: compact bone and spongy bone. Compact bone has a denser

histological arrangement making it stronger than spongy bone. As a result, compact bone will

form the outer layer of a bone organ while spongy bone forms the inner aspect of the bone organ.

Sometimes they are referred to as cortical bone and medullary bone respectively.

Compact Bone Tissue

Spongy Bone Tissue

There are four classes of bone organs based on shape: long bones, short bones, flat bones,

and irregular bones. Long bones are longer than they are wide. As we shall see, long bones will

have a distinctive internal architecture that distinguishes them from the other three classes. Long

bones include the femur and humerus. Short bones are simply that, short. They include many of

the carpal and tarsal bones (ex; pisiform, first cuneiform). There is a subclass of short bone

called the sesamoid bones. Sesamoid bones are short bones that do not attach to the skeleton

directly. Instead they are enveloped in tendon and ligament and attach indirectly to the

skeleton. Sesamoid bones are named for their sesame seed like shape. An example of a

sesamoid bone is the patella. Flat bones are thin, flattened bones. They include many of the

bones of the skull (ex; parietal) and the ribs. Certain flat bones have evolved an elongated

appearance (ex; ribs, clavicle) and may be confused with long bones initially. However their

internal structure is clearly not that of a long bone. Irregular bones are oddly shaped bones that

do not fit into the other three classes. They include the vertebrae.

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The Four Classes of Bone Organs Based On Shape

Long bones have a distinctive structure. The rounded ends of a long bone, commonly

called “heads”, are termed epiphysis. The epiphysis that is closer to the main axis of the body is

called the proximal epiphysis. The epiphysis that is further from the main axis of the body is

called the distal epiphysis. Between the two epiphyses is the shaft of the bone anatomically

called the diaphysis. Internally both the epiphyses and the diaphysis have an outer layer of

cortical bone composed of compact bone tissue. In the epiphyses, internal to the cortical bone,

we see an extensive proliferation of spongy bone tissue forming the medullary bone. Within the

intertrabecular spaces red marrow is found. Red marrow is a hemopoietic tissue meaning that it

produces blood cells. In the diaphysis, internal to the cortical bone, we see very little spongy

bone. Instead there is a large open space called the medullary cavity. The medullary cavity is

filled with yellow marrow primarily. Yellow marrow is a densely packed adipose tissue.

In growing bone there exists a plate of hyaline cartilage between the epiphysis and the

diaphysis called the epiphyseal plate or epiphyseal growth plate . This is the region from which

the bone lengthens until an individual hits maturity. When growth stops the cartilaginous plate

ossifies and remains as a line of compact bone tissues situated between the diaphysis and the

epiphysis. This structure is termed the epiphyseal line.

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Sagittal Section of a Long Bone

Covering the external surface of the bone organ is a connective tissue sheath called the

periosteum. The periosteum has two layers that are similar to those of the perichondrium. The

outer layer is a tough fibrous connective tissue. Extensions of this fibrous layer form ligaments

and play a role in forming tendons. Internally the periosteum has a single layer of multipotent

cells that can produce new bone cells and repair and remodel the bone organ. The periosteum is

attached to the bone by fibers called perforating fibers. Lining the internal surfaces of the bone

organ is the endosteum. The endosteum is similar to the inner layer of the periosteum. It is a

single layer of multipotent cells that can produce new bone cells and repair the bone organ.

The other three classes of bone organs have a very similar internal architecture to one

another. They have an outer layer of cortical bone (compact bone tissue) surrounding an inner

layer of medullary bone (spongy bone). The spongy bone houses red marrow. The other three

classes of bone organ lack: epiphyses, diaphysis, and a medullary cavity. Like long bones they

are covered by periosteum externally and endosteum internally.

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Chapter 1. Table 1 Basic Terminology For Osteology

The following list covers many of the terms that you will come across as you study

osteology.! An understanding of these terms prior to entering the lab should make your study

time more efficient and effective.

(1) Foramen – a hole (ex; foramen magnum).

!!!!!!!!!!! (2) Fissure - a long narrow, opening in a bone (ex; superior orbital fissure).

(3) Meatus - meaning “canal” this is a canal-like opening in a bone (ex; external acoustic

meatus).! Often the term “canal” can be used interchangeably with “meatus”.

!!!!!!!!!!! (4) Fossa - a depression on the surface of a bone (ex; anterior cranial fossa).

!!!!!!!!!!! (5) Fovea - a pit in the surface of a bone (ex; fovea capitis).

(6) Sulcus - a groove on the surface of a bone (ex; lacrimal sulcus).! Often the term

“groove” can be used interchangeably with “sulcus”.

!!!!!!!!!!! (7) Tubercle - a rounded elevation on a bone (ex; pubic tubercle).

(8) Tuberosity -a roughened elevation on the surface of a bone (ex; ischial tuberosity).! In

certain cases the terms “tubercle” and “tuberosity” may be used interchangeably.

(9) Line - a line on the surface of a bone, a shallow linear elevation on the surface of a

bone (ex; soleal line).

(10) Crest - a linear elevation on the surface of a bone (ex; intertrochanteric crest).! A

crest will be a higher linear elevation than is a line.

(11) Process - an extension of a bone (ex; zygomatic process of the temporal bone)! If a

process attaches to another bone it will be named for the bone to which it articulates

(ex; temporal process of the zygomatic bone)..

(12) Condyle - a flared extension on a long bone that allows for better articulation (ex;

medial condyle of femur). Condyles allow for direct bone to bone attachment.! They

greatly increase! the surface area for an articulation adding to the strength and

stability of a joint.

(13) Condyloid - a condyle-like structure found on a bone that is not a long bone

(ex; condyloid process of the mandible).

!!!!!!!!!!! (14) Epicondyle - an elevation situated on a condyle (ex; medial epicondyle of the !!!!!!!!!!!

femur).! They allow for indirect bone to bone attachment (by serving as the !!!!!!!!!!

!!!!!!!!!!! anchoring point for ligaments) and for muscle attachment.

(15) Coronoid - a wing-like extension of a bone (ex; coronoid process of the ulna).

(16) Coracoid - meaning “crow’s beak” this is an extension of a bone that resembles the

bill of a crow (ex; coracoid process of the scapula).

!!!!!!!!!!! (17) Malleolus - a flattened projection (ex; medial malleolus of tibia).

!!!!!!!!!!! (18) Ramus - a bridge-like structure (ex; superior pubic ramus).

!!!!!!!!!!! (19) Ala - a wing shaped surface of a bone (ex; ala of sacrum).

(20) Facet - means an articulating surface (ex; superior articulating facet of vertebra).!

The terms “facet” and “articulating surface” can be used interchangeably.

(21) Demifacet - half of an articulating surface (ex; demifacet on body of a

thoracic vertebra).

(22) Cornu - meaning “horn”, it is a horn-like extension off of a bone (ex; sacral cornu)

!

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!

Chapter 1: Skeletal Structure

Part B: The Axial Skeleton

Topic B1: The Vertebrae

In vertebrates vertebrae can be composed of either cartilage or, more commonly, bone.

They are successively arranged to form the vertebral column. The vertebral column surrounds

and protects the spinal cord, serves as a point of attachment for ligaments, tendons, and muscles,

and helps to bear the weight of the body.

Mammalian Vertebrae Demonstrating Some Basic Features

The modern vertebra typically consists of a centrum, a neural arch (aka; vertebral arch),

and one or more process (aka; apophyses) that project from either the centrum or the arch. The

centrum occupies the position occupied by the notochord during development. Due to their

method of development the vertebral centra are located intersegmentally, between two

myomeres. They develop along the notochord that had defined the long axis of the developing

embryo. The degree to which the notochord is maintained throughout an organism’s life varies.

The notochord may begin regression with the development of the vertebrae. The neural, or

vertebral, arch is located dorsal to the centrum. The vertebral arch serves to protect the spinal

cord. Successive arches, and their connecting ligaments, form the neural/vertebral canal. The

base of the arch is termed the pedicle and the roof and sides of the arch are termed the lamina.

Along with the vertebral arch some vertebrates will have vertebrae possessing a hemal arch.

When present the hemal arches are located in the tail, ventral to the centra and will house the

caudal artery. In amniotes they are called chevron bones.

The number and types of apophyses vary between vertebrate groups. Chondrichthyes can

be considered to have basal vertebrae since theirs have only one pair of apophysis. Mammals on

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the other hand have numerous, well developed apophyses. The diapophyses (or transverse

processes) are the most common vertebral process. They articulate with ribs and serve for muscle

and ligament attachment (as do all of the apophyses to some degree). Another paired lateral

apophysis off of the centrum is the parapophyses. Parapophyses occur in vertebrates that have

biccipital ribs such as Necturus. (“Biccipital” means “two –headed”). The two heads are the

capitulum and tubercle. The parapophysis will attach to the capitulum of the rib. The tuberculum

of the rib will attach to the diapophysis of the vertebrae. Zygapophyses (or articulating

processes) allow for articulation between successive vertebrae. The typical vertebra will have

two pairs of zygapophyses. Located on the cranial aspect of the vertebra are the

prezygapophyses (a.k.a.; cranial articulating processes, superior articulating processes). These

are paired structures that allow one vertebra to attach to the vertebra cranial to it.

Postzygapophyses (a.k.a.; caudal articulating processes, inferior articulating processes) are

paired structures on the caudal aspect of the vertebrae that allow one vertebra to attach to the

vertebra caudal to it.

Squalus displays the typical chondrichthyan vertebra. The vertebrae are composed of

cartilage and consist of a centrum and vertebral arch. The chondrichthyan vertebrae are

considered to be the model for the primative vertebrate vertebrae. Although agnathans are more

primative and the vertebrae of extant species are considered to be incomplete, their placement in

the evolution of the vertebral column is speculative. The current agnathans vertebrae may

represent an early stage of vertebral development. However it is equally likely that the vertebrae

of extant species represents a derived characteristic; that the vertebrae have been reduced in

complexity over time.

Diapophysis

Dorsal Plate of Neural Arch

Dorsal Intercalary Plate of Neural Arch

Centrum

Ventral Plate Ventral Intercalary Plate

Trunk Vertebrae Caudal Vertebrae

Squalus Vertebrae

As is true for all fishes the vertebrae are divided into only two regional groups: trunk and

caudal. They are easily distinguishable. The trunk vertebrae possess poorly defined transverse

processes. In Squalus the trunk vertebrae will articulate with ribs. The caudal vertebrae have

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hemal arches and do not articulate with ribs. The caudal vertebrae also display dispondyly.

Dispondyly means that there are two centra and two sets of neural and hemal arches in each tail

metamere. As a result the number of caudal centra is double that of caudal myomeres and caudal

spinal nerve pairs.

In sharks the notochord is retained in the adult. It is found throughout the length of the

vertebral column, where it is restricted to the centra. Shark centra are amphicelous being concave

at both ends. The vertebral arch consists of paired dorsal plates that will join to form the

vertebral arch. Between the arches are paired dorsal intercalary plates. The vertebral canal is

composed of the dorsal plates and the interdigitating dorsal intercalary plates. The dorsal

intercalary plates will each have a pair of perforations called the intervertebral foramina. These

openings allow for the passage of the spinal nerves. The caudal vertebrae will also have hemal

arches consisting of paired ventral plates. As occurred with the vertebral canal, between the

hemal arches are paired ventral intercalary plates. The ventral plates and the ventral intercalary

plates will form the hemal canal for the caudal artery.

Like Squalus the vertebrae of Necturus are amphicelous. Necturus, however, has a

vertebral column that shows a greater degree of regional differentiation than was seen in

Squalus. Along with trunk and caudal vertebrae there are one cervical vertebra and one sacral

vertebra. The cervical vertebra is a trunk vertebra that is modified to articulate with the occipital

condyles of the skull. This is the first step in the evolution of a neck, a tetrapod feature. The

cervical vertebra does not articulate with ribs. The sacral vertebra is a trunk vertebra that, like

the other trunk vertebrae, articulates with a pair of ribs. This rib pair is unique, however. These

are the sacral ribs. Sacral ribs articulate with the ilium of the pelvis.

Caudal Vertebrae Sacral Vertebra Trunk Vertebrae Cervical Vertebra

Necturus Demonstrating Regional Vertebral Variation

The trunk vertebrae of Necturus each have a pair of prezygapophyses and

postzygapophyses, a spinous process, a centrum, and a vertebral arch that will enclose the

vertebral canal. They will also have two pairs of processes to articulate with the biccipital ribs of

urodeles. They have a pair of diapophyses to articulate with the tuberculum of the rib and a pair

of parapophyses to articulate with the capitulum of the rib. This pattern is also true for the sacral

vertebra since the sacral ribs are also biccipital.

The caudal vertebrae show some variation. The first five resemble smaller trunk

vertebrae complete with parapophyses and diapophyses. After the fifth caudal vertebrae the

vertebrae more closely resemble the caudal vertebrae typical of fish. They will possess a hemal

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arch to enclose the hemal canal and a vertebral arch. The diapophyses and parapophyses are lost

and the prezygapophyses and postzygapophyses are reduced.

Dorsal View: Prezygapophysis Neural Spine Postzygapophysis Parapophysis Diapophysis

Ventral View: Centrum Transverse Process

Necturus Trunk Vertebrae

Amniotes have a vertebral column showing a much greater degree of regional

specialization than that of other vertebrates. This can easily be seen in Felis. To deal with life on

land the vertebral column became specialized into five subdivisions. Cervical vertebrae are

located in the neck and are designed to increase head movement. Thoracic vertebrae are located

in the upper to mid-back. They are associated with long ribs designed to protect the viscera.

These vertebrae also provide some support for the pectoral girdle. Lumbar vertebrae are the

vertebrae of the lower back. Sacral vertebrae serve to support the pelvic girdle. Caudal vertebrae,

as we have seen previously, are the vertebrae of the tail.

All five regional classes of vertebrae have been modified over evolutionary time to better

perform different duties. As a result, they will have morphological features that should allow

you to distinguish between them. Cervical vertebrae can be differentiated from the other

regional classes by the presences of transverse foramen, holes in the diapophyses/transverse

processes. The transverse foramina allow for passage of the vertebral artery. Cervical vertebrae

tend to show the greatest degree of variation between one another. In amniotes the number of

cervical vertebrae is greater than what we saw in Necturus giving a longer, more flexible neck.

Felis, and most mammals, will have seven cervical vertebrae. They are often referred to by the

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Representatives of the Five Regional Types of Vertebrae in Felis

Typical Feline Cervical Vertebra, Cranial View

letter “C” and the number of their placement. For example, the first cervical vertebra can be

called “C1”. The first and second cervical vertebrae are modified to increase movement of the

head on the neck. C1 (a.k.a.; atlas) is a ring-shaped bone lacking most of the centrum. The

cranial articulating processes are well developed to articulate with the skull. In Felis they

articulate with the two occipital condyles of the skull. (there is only one occipital condyle in

reptilian and avian skulls.) C2 (or axis) is a modified vertebra having a cranially projecting

process called the dens or odontoid process. The dens is actually the centrum of C1

that detached from C1 and fused to C2 during development. The dens allows for the head to

pivot on the neck

19

Felis C1, The Atlas, Ventral View

Felis C2, The Axis, Lateral View

20

The thoracic vertebrae are the most numerous regional type of vertebra at thirteen and

show some variation. They can be identified by a facet on transverse process for the tubercle of

a rib, and facets/demifacets on the body for the head of the rib. The presence of facets on the

transverse processes and facets or demifacets on the centra is due to the fact that all thoracic

vertebrae articulate with the ribs. The last two thoracic vertebrae and the first lumbar resemble

each other quite a bit. Look for the presence (or absence) of facets on their bodies to distinguish

them. Most times the head of one rib will overlap between two adjacent bodies. When this

occurs each body has half an articulating surface, a demifacet, of the half a rib head that it is

articulating with. Facets can be distinguished from demifacets by appearance (facets look like

full moons and demifacets resemble half moons) and relative location (demifacets are near the

edge of the body). Facets are found on the bodies of T1, T12, and T13. Demifacets are found on

the bodies of T1 through T11. (T1 attaches to ribs R1 and R2.)

Typical Feline Thoracic Vertebrae, Cranial View

There are seven lumbar vertebrae in Felis. Lumbar vertebrae are larger than are thoracic

vertebrae. They have larger centra and processes. This as a structural adaptation since they bear a

21

Felis Thorax Demonstrating a Demifacet

great deal of weight and still must have articulations that allow for a good range of motion in the

lower back. In addition they have mammillary and accessory processes/bodies. The

mammillary body is a rounded elevation on the cranial articulating process. The accessory

process is a more linear elevation that is near the caudal articulating process. The combination

of the accessory and caudal articulating processes allows for better articulation with the cranial

articulating process on the next vertebra. The more caudally located lumbar vertebrae have long,

cranially pointed transverse processes that help to anchor the erector spinae muscles

Typical Feline Lumbar Vertebra, Lateral View

22

Cats possess three sacral vertebrae. These three vertebrae fuse together to form the

sacrum. Although S1 is a large bone, S2 and S3 show a reduction in size. This is due to the fact

that the sacrum articulates with the innominate bones. The pelvis takes over the bulk of the

weight-bearing role. Before identifying the features of the sacrum, you should take the time to

examine S1 and to identify the basic vertebral features.

Felis Sacrum

To deal with its role in the pelvic girdle the sacrum has a number of specialized features.

The easiest to observe is the lateral mass. The lateral mass is actually the fused transverse

processes of the three sacral vertebrae. They are designed to improve the articulation and

weight-bearing role of the iliosacral joint. The descriptive term for the cranial surface of the

lateral mass is ala since it resembles the wing of a bird. The roughened portion of the lateral

mass, where it joins with a correspondingly shaped surface on the ilium (to form the iliosacral

joint), is termed the articular surface. The articular surface loosely resembles a human ear and so

can be referred to as “auricular surface”. (Auricle, or pinna, is the anatomical term for what is

commonly called the “ear”.) The sacral crests are linear elevations found on the dorsal aspect of

the sacrum. One is the median sacral crest. It is a singular elevation formed from the sacral

spinous processes. There are also a pair of lateral sacral crests. These are linear elevations on

the lateral mass. A third set of sacral crest are the paired articular/auricular sacral crests. This is

another pair of linear elevations of the lateral mass located lateral to the lateral sacral crest and

located immediately dorsal to the articular surface. These sacral crests serve as anchoring points

of the erector spinae muscles.

The sacrum is shaped much like an inverted arrowhead. The point of the arrowhead is

termed the apex of the sacrum. There is an opening near the apex of the sacrum called the sacral

hiatus. The sacral hiatus allows for passage of the spinal nerves. This purpose is also served by

the sacral foramina. Sacral foramina are openings between adjacent sacral vertebrae by which the

23

sacral spinal nerves exit the vertebral column. Sacral foramina are the intervertebral foramina of

the sacrum. Flanking the sacral hiatus are horn-like projections called sacral cornua. The sacral

cornua point caudally so as to attach to the first caudal vertebrae by ligaments.

The caudal vertebrae of cats are variable in number. Those located closest to the sacrum

resemble smaller versions of the lumbar vertebrae and show the typical apophyses. The more

distal caudal vertebrae have a very reduced structure. They are centra having reduced

zygapophyses (the role being taken over by ligaments) and a dorsally incomplete vertebral arch.

The caudal vertebrae of Felis will have hemal arches. These inverted “V-shaped” osseous

structures tend to detach from the vertebrae. Due to their appearance they are termed chevron

bones.

Topic B2: The Ribs and Sternum

Ribs are flat bones that articulate with the vertebrae and extend into the body wall. They

are formed intersegmentally, as are vertebral centra. True ribs arise by endochondral

ossification. Some reptiles possess abdominal ribs (a.k.a.; gastralia). These ribs do not arise

endochondrally and so are not considered to be true ribs. Some fishes have two sets of ribs,

dorsal and ventral ribs, associated with each trunk vertebrae. Dorsal ribs project laterally into the

body wall and into the skeletogenous septum. The skeletogenous septum is a collagenous

structure that divides the epaxial and hypaxial muscle groups. Ventral ribs project ventrally as do

mammalian ribs. The occurrence of these ribs varies among fishes. Most fishes have only

ventral ribs. Sharks and a few other fishes have only dorsal ribs. Although the ventral ribs are

positioned where tetrapod ribs are located it is believed that the dorsal ribs of fishes actually gave

rise to the tetrapod rib.

In Squalus the ribs are dorsal ribs. They are short cartilaginous structures that project

into the skeletogenous septum. They articulate with the transverse processes of the trunk

vertebrae.

Squalus Ribs Necturus Ribs

24

In Necturus the ribs are also short structures that project into the skeletogenous septum.

The ribs of urodeles are biccipital meaning “two headed”. The two heads both are on the

vertebral extremity of the rib and are the capitulum and tuberculum. The capitulum articulates

with the parapophysis of the trunk vertebrae. The tuberculum articulates with the diapophysis of

the trunk vertebrae.

In Felis the ribs typically attach at two locations: the thoracic vertebrae and the sternum.

Although not all of the ribs attach to the sternum, most do and many of those will attach by a

cartilage called costal cartilage. Mammal ribs have reduced the Y-shape of the biccipital ribs

found in their reptilian ancestors. The capitulum has become a shorter, more rounded structure

termed the head. The tuberculum has been reduced to a small, round elevation on the neck of the

rib called the tubercle. Both are on the vertebral extremity of the rib. The rib extends ventrally

towards the sternum. As it does it bends closer to the midline. This curve is called the angle.

The sternal extremity attaches to the sternum either by its own costal cartilage (vertebrosternal),

by its costal cartilage attaching to the costal cartilage of a rib cranial to it (vertebrochondral) or

not at all (vertebral).

Vertebral Extremity:

Angle Tubercle Neck Head

Sternal Extremity

Felis Rib Felis Thorax Showing the Sternum

The sternum is found only in tetrapods. Its presence, size, and anatomical features

correlate to the extent that the front limbs are used in locomotion. In most mammals the sternum

is composed of bony plates called sternebrae. Felis has seven sternebrae. The first is called the

manubrium. The last sternebra is termed the xiphisternum. Attached to the xiphisternum, is the

xiphoid. The xiphoid is one of the last skeletal features to ossify. (In humans it ossifies at about

the age of 45.)

25

Topic B3: The Skull

The skull is a complex structure. In comparative vertebrate anatomy the term ”skull” can

be divided into the cranial skeleton and the visceral skeleton. The cranial skeleton is the skull

proper. It can be thought of as the skull minus the jaw. There are two components to the cranial

skeleton: the neurocranium and the dermatocranium. Joints called sutures typically join the

bones of the skull.

The neurocranium is the primary brain case. The neurocranium is also referred to as the

chondrocranium, or endocranium. The neurocranium protects the brain and certain special senses

such as vision and olfaction. It is composed of cartilage in primitive vertebrates such as Squalus.

Over evolutionary time it has become increasingly ossified. The neurocranium begins as

cartilage and is subsequently partially or completely replaced by bone in all vertebrates

excepting the chondrichthyes. For this reason the neurocranium of chondrichthyes is referred to

as the chondrocranium. As a result, the bony component of the neurocranium is composed of

bones that have formed by endochondral ossification

Primitive vertebrates had bones in the integument that were part of a protective covering

termed dermal armor. The integumentary bones of the head migrated subdermally to form the

dermatocranium. Since these bones were once integumentary structures that developed by

intramembranous ossification, the bones of the dermatocranium today will also arise by

intramembranous ossification.

The visceral skeleton is also known as the splanchnocranium. As was the case with the

neurocranium, it is composed of cartilage in primitive vertebrates. It also became ossified as

membrane bones were added from the integument surrounding the skull. The splanchnocranium

is composed of four skeletal structures. One is the embryonic upper jaw cartilage called the

palatopterygoquadrate and its replacement bones. A second is the embryonic lower jaw cartilage

called the Meckel’s cartilage and its replacement bones. A third is the skeleton of the

Squalus Chondrocranium (white tagged) and Splanchnocranium (green tagged)

26

hyoid. A fourth is the skeleton of the branchial arches, the gill arches and their derivatives in

tetrapods.

27

The skull of Squalus consists of the chondrocranium and the splanchnocranium. Both the

chondrocranium and splanchnocranium of chondrichthyes are composed entirely of cartilage in

the adult. The only exception is the teeth. In sharks and rays the neurocranium demonstrates

complete fusion of all its components into a singular cartilaginous structure, the chondrocranium.

Some other fishes have a primarily cartilaginous neurocranium in the adult (ex; sturgeons).

However, they lack a complete roof, or tectum, of cartilage to protect the brain. This role is

handled by the dermatocranium. Squalus, as is true for all sharks and rays, lacks a

dermatocranium.

The walls of the chondrocranium are fully developed in the adult and include a posterior

occipital wall that is lacking in agnathans. The occipital wall of the chondrocranium will have an

opening for the spinal cord called the foramen magnum. On each side of the foramen magnum

will be the occipital condyles that will articulate with the first vertebra. The chondrocranium will

house and protect the brain and some of the special senses. It will have a pair of orbits in which

the eyes are located. The orbit will not fuse to the chondrocranium to allow for movement of the

eye. The orbit is bracketed by the anterior orbital process, supraorbital crest, and postorbital

processes dorsally and the antorbital shelf and infraorbital shelf ventrally running cranial to

caudal in both cases. It also contains a small mushroom-shaped structure called the optic

pedicle. The capsules of those special senses that do not require movement to function will fuse

Olfactory Capsule (damaged) Deep Ophthalmic Foramen

Olfactory Foramen Trochlear Foramen Trigeminofacial Foramen

Optic Foramen Occulomotor Foramen Hyomandibular Foramen

Basal Plate showing Notochord

Squalus – Chondrocranium, Lateral View Showing Foramina

28

to the chondrocranium. The otic capsules house the internal ear and are fully fused to the

posteriolateral walls. The internal ear allows for the sensation of hearing, static equilibrium, and

dynamic equilibrium. The olfactory capsules are fully fused to the anteriolateral walls and will

contain the olfactory bulbs.

The floor of the chondrocranium is composed of the basal plate and the ethmoid plate.

The basal plate will fuse to the otic capsules during development. It will contain the notochord.

The notochord is visible as a ridge extending cranially from the foramen magnum on the ventral

aspect of the chondrocranium. An opening will remain in the chondrocranium where the basal

and ethmoid plates fused during development. This opening is the hypophyseal fenestra. This

opening remains to accommodate the carotid arteries and the pituitary gland (aka; hypophysis).

The portion of the opening visible on the ventral surface of the chondrocranium is the carotid

canal. The hypophyseal fenestra has developed a saddle shaped structure called the sella turcica

to house the pituitary gland. The ethmoid plate component of the floor of the chondrocranium is

fused to the olfactory capsules. The ethmoid plate will extend anterior to the olfactory capsules

as a blade-like extension called the rostrum. The rostrum will support the snout of the shark and

is very thin walled. The rostrum is the final portion of the chondrocranium to chondrify,

especially at the junction between the rostrum and the rest of the chondrocranium.

Olfactory Capsule Rostral Fenestra Precerebral Cavity Epiphyseal Foramen

Endolymphatic Foramen Endolymphatic Fossa Perilymphatic Foramen

Squalus-Dorsal Chondrocranium Showing Foramina

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Otic Capsule Optic Pedicle Supraotic Crest Postorbital Process Supraorbital Crest

Hyomandibular Foramen Trigeminofacial Foramen Optic Foramen

Squalus-Chondrocranium Showing Optic Pedicle

The chondrocranium will have a number of openings to allow for passage of blood

vessels and nerves. These include the olfactory foramina on the anterior aspect of the olfactory

capsules. There are a number of foramina associated with the orbit. They include the superficial

ophthalmic foramina, deep ophthalmic foramina, occulomotor foramina, optic canals, trochlear

foramina, and trigeminofacial foramina. Dorsal and medial to the orbits will be the epiphyseal

foramen. On the posteriodorsal aspect of the chondrocranium is a depression called the

endolymphatic fossa that will house endolymphatic foramina and a second depression called the

perilymphatic fossa that will house the perilymphatic foramina. The otic capsule will have the

hyomandibular foramina (to anchor the articulation of the hyomandibula with the

chondrocranium). A pair of extensions will be found on the caudal aspect of the otic capsule

called the postotic processes. These processes will each have an opening covered by a thin plate

of cartilage termed the postotic fenestra. Between the postotic process and foramen magnum will

be the glossopharyngeal foramen and the vagus canal respectively.

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Centrum of First Vertebra Vagus Foramen Postotic Process

Occipital Condyle Foramen Magnum Glossopharyngeal Foramen Postotic Fenestra

Squalus – Chondrocranium, Posterior View (upside down)

The visceral skeleton, or splanchnocranium, derives from the pharyngeal arches. In

fishes the splanchnocranium forms the jaws and gill arches. In Squalus the splanchnocranium

consists of the cartilages of each pharyngeal arch and the median basihyal and basibranchial

cartilages of the pharyngeal floor. The skeleton of each arch follows very closely to a basic

pattern. All but the first and last pharyngeal arches support gills.

The first pharyngeal arch is called the mandibular arch and forms the jaws. The

mandibular arch is a pharyngeal arch that has been modified for feeding. It consists of two

cartilages forming the upper and lower jaw respectively. The palatopterygoquadrate cartilage

forms the upper jaw. It has two pairs of processes. One pair of processes enters into the orbits

(one process per orbit) and so they are termed the orbital processes. There is also a pair of

quadrate processes, each projecting laterally. The quadrate cartilages, along with the

hyomandibula, are responsible for the suspension of the jaws from the chondrocranium. The

lower jaw is composed of Meckel’s cartilage. It will articulate with the palatopterygoquadrate

and the hyoid on each side. A pair of slender labial cartilages flanks the jaws. They have no

known function.

The second pharyngeal arch is called the hyoid arch. It is also a modified pharyngeal arch

although its role in feeding is more limited. The hyoid arch consists of 5 cartilages: 1

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Occipital Condyle Postotic Process Postorbital Process Antorbital Process

Basal Plate Postorbital Shelf Antorbital Shelf

Supraotic Crest Carotid Foramen Supraorbital Crest Rostral Fenestra Rostral Carina

Superficial Ophthalmic Foramina

Squalus-Chondrocranium, Ventral View

singular and 2 paired groups. Dorsally are the right and left hyomandibular cartilages /

hyomandibulae. These are short cartilages that articulate with the posterior aspect of the

chondrocranium. Immediately below the hyomandibular cartilages are the right and left

ceratohyal cartilages. The ceratohyal cartilages bear gills and extend under the chondrocranium.

The ventral aspects of the ceratohyal cartilages attach with the singular basihyal cartilage located

midventrally. Meckel’s cartilage and the palatopterygoquadrate cartilage articulate with each

other at the angle of the mouth and will also articulate with the hyomandibular cartilages of the

hyoid arch. Ligaments support these articulations. The hyomandibulae are bound by ligaments to

the otic capsules and suspends the jaws and the entire branchial skeleton from the

chondrocranium. This is an example of a hyostolic jaw suspension.

Pharyngeal arches 3 through 7 have the same basic structure. All but #7 bear gills. The

dorsal most portion of these pharyngeal arches are the pharyngobranchial cartilages. The

pharyngobranchial cartilages attach ventrally to the epibranchial cartilages. The epibranchial

cartilages attach ventrally to the ceratobranchial cartilages. Both the epibranchial and

32

ceratobranchial cartilages typically will bear gill rakers and gill rays. The ceratobranchial

cartilages attach ventrally to the hypobranchial cartilages. The paired hypobranchial cartilages

attach to the singular, midventrally located basibranchial cartilage. There are only two

basibranchial cartilages. The third pharyngeal arch attaches to the first basibranchial while

arches 4 through 7 share a common, larger basibranchial cartilage.

First Visceral Arch: Palatopterygoquadrate + Meckel’s Cartilage

First Epibranchial Last Pharyngeobranchial

Second Visceral Arch: Basihyal + Ceratohyal + Hyomandibula Gill Rays

Squalus- Splanchnocranium, Lateral View

33

First Visceral Arch: Meckel’s Cartilage + Palatopterygoquadrate

Second Visceral Arch: Ceratohyal + Basihyal

First Ceratobranchial First Hypobranchial Basibranchial

Squalus-Visceral Splanchnocranium

34

Otic Capsule Quadrate Process Orbital Process Antorbital Process Antorbital Shelf

Palatopterygoquadrate Meckel’s Cartilage Labial Cartilage (encased in flesh)

Squalus Chondrocranium and Splanchnocranium Showing Jaw Articulation

In Necturus the skull consists of the splanchnocranium and neurocranium. Unlike

Squalus, the neurocranium of Necturus is mostly ossified and consists of both endochondral and

membrane bones. The endochondral bones derive from components of the cartilaginous

chondrocranium during development. The membrane bones are homologous to the dermal

armor of more primitive vertebrates and so are collectively called the dermatocranium. As a

result the neurocranium of Necturus is also referred to as the “neurocranial-dermatocranial

complex”.

The neurocranium of the developing Necturus is initially entirely cartilaginous. Some of

these cartilages are maintained in the adult (such as the antorbital cartilages) but many are

replaced by bone through endochondral ossification. As is the case with Squalus, the floor of the

cartilaginous neurocranium includes the ethmoid plate. This plate will partly ossify to give the

ethmoid bone. Posteriolateral to the ethmoid plate will be the right and left quadrate cartilages.

The quadrate bones will replace these paired cartilages. The quadrate bones will articulate with

the right and left palatopterygoid bones (one of the dermal bones that will ensheath the

palatopterygoquadrate cartilage). Posterior to the quadrate cartilages in the developing skull will

be the otic capsules. They will include the prootic and opisthotic cartilages, which will be

replaced by the prootic and opisthotic bones respectively. Between them will be some remnant

35

cartilage in the adult. This cartilage has a perforation called the fenestra ovalis. The fenestra

ovalis will be covered by a membrane (the internal tympanic membrane) on which sits the

columnella/stapes. The columnella is the first auditory ossicle to appear in vertebrates. It will

have a tiny, spike-like projection called the stylus and will conduct sounds waves into the otic

capsule. (Note: the quadrate bone will become one of the mammalian ossicles, the incus.)

Caudal and medial to the otic capsules will be the foramen magnum and the cartilages that

surround it. These cartilages will be the supraoccipital arch, basioccipital arch, and exoccipitals.

Through endochondral ossification the supraoccipital, basioccipital, and exoccipital bones will

replace these cartilages respectively. The exoccipital bones will possess the occipital condyles to

articulate with the cervical vertebra.

Exoccipital Parietal Squamosal Quadrate Palatopterygoid Frontal Premaxilla

Otic Capsule

Necturus – Skull, Dorsal View

The dermatocranium will include bones that will ensheath the palatopterygoquadrate

cartilage to form the new upper jaw. These bones include the premaxillae, vomers (which also

form a portion of the primary palate), and palatopterygoids (which articulate with the quadrate

bones). All of these bones bear teeth. The roof of the skull is formed by the frontal and parietal

bones. The parietal bone will form the roof of the otic capsule. Lateral to the parietal bone will

36

be the squamosal. The squamosal will articulate with the quadrate anteriorly. The floor of the

skull will be ensheathed by the dermatocranial bone called the parasphenoid. The parasphenoid,

along with the vomers, will form the primary palate. The parasphenoid and parietals will obscure

the basioccipital and supraoccipital bones respectively.

Epibranchials Squamosal Quadrate Angular Palatopterygoid Dentary Premaxilla

Opisthotic Parietal Frontal

Necturus – Skull, Dorsal View 2

37

Premaxilla Vomer Frontal Palatopterygoid Parietal Squamosal

Dentary Splenial Meckel’s Cartilage Angular Quadrate

Necturus – Skull, Lateral View

Exoccipital Foramen Magnum

Necturus – Skull, Posterior View

38

Premaxilla Ethmoid Vomer Parasphenoid Prootic Fenestra Ovalis Opisthotic

Palatopterygoid Quadrate Squamosal Stylus Columnella Exoccipital

Necturus– Skull, Ventral View

The splanchnocranium of Necturus includes the jaws, hyoid, and gill arches. The hyoid

and gill arches remain as cartilage throughout the life of the mudpuppy. The cartilages of the

embryonic jaws will become ensheathed in bone derived from dermal armor. As we have

already seen, the palatopterygoquadrate becomes encased in the premaxillae, vomers, and

palatopterygoid (some times referred to as the “pterygoid”). The dentary, splenial, and angular

bones will cover most of the Meckel’s cartilage of the lower jaw. Some Meckel’s cartilage will

remain near the jaw joint above the angular. The jaw joint is between the angular and quadrate

bones. Both the dentary and splenial will bear teeth. The dentary is equivalent to the

mammalian mandible. The mandibular arch is the first visceral arch.

The hyoid arch will be composed of two pairs of cartilages. The basal cartilage pair is

the hypohyals that will attach to the first basibranchial cartilage of the gill arches. Attached to

the hypohyals will be the ceratohyals. The hyoid comprises the second visceral arch.

39

Angular Meckel’s Cartilage Splenial Dentary Mental Symphysis

Angular Dentary

Necturus Mandible

(Top-Left, Internal View Bottom-Right, External View)

Necturus possesses three pairs of gills (visceral arches 3, 4, and 5). Their skeletal

structures are cartilaginous throughout life. Unlike the gills of Squalus, the gills of Necturus are

external. These structures can be moved by muscles to better direct them into water currents so

as to pick up more oxygen. The first gill arch pair is the best developed. The second and third

are anchored on to the first. The skeleton of the gills in Necturus has two basibranchial

cartilages. One is larger and anterior to the other. This first basibranchial cartilage will attach to

the hyoid and the first pair of ceratobranchial cartilages. The second basibranchial will be partly

ossified and attaches only to the first basibranchial. There are two pairs of ceratobranchial

cartilages. The first pair is large and well developed. They will attach to the first basibranchial

cartilage inferiorly and the first pair of epibranchial cartilages superiorly. The second pair of

ceratobranchial is very reduced and attach to the first ceratobranchials. These cartilages support

the second and third pairs of epibranchials. There are three pairs of epibranchial cartilages. The

first pair attached to the first ceratobranchial cartilages while the second and third pair attach to

the second ceratobranchials. The first epibranchial is the largest of the three and the third is the

smallest.

40

Dentary Splenial Angular Ceratohyal Basibranchial 2 Ceratobranchial1 & 2

Hypohyal Basibranchial 1 Epibranchial 1, 2, & 3

Note; Viscera Arch 1 = Jaws/Mandibular Arch

Visceral Arch 2 = Hyoid/Hyoid Arch

Visceral Arch 3 = Ceratobranchial 1 + Epibranchial 1

Visceral Arch 4 = Ceratobranchial 2 + Epibranchial 2

Visceral Arch 5 = Ceratobranchial 2 + Epibranchial 3

Necturus - Splanchnocranium

The skull of Felis is more complex that that of either Necturus or Squalus. Mammalian

skulls have evolved features that will differentiate them from the skulls of other vertebrates.

There are four developments distinguishing mammalian skulls. One is the development of the

dentary as the only bone of the lower jaw. A second is an altered site of articulation for the

lower jaw. This ties in with the third development, the presence of three pairs of auditory

ossicles. A fourth development is alterations of the secondary palate (Note: Squalus and

Necturus have only a primary palate). The secondary palate separates the nasal and oral cavities.

The neurocranium is incomplete dorsally resulting in the presence of fontanels in the skull of

a newly born mammal. These fontanels allow for increased growth of the skull and the ability of

41

Some Features of the Skull in Felis

the skull to pass through the birth canal. Endochondral ossification of the neurocranium will

result in a number of bones. The neurocranium contributes the basioccipital, basisphenoid, and

presphenoid bones to form the floor of the cranium. It will also contribute a portion of the lateral

walls of the cranium with the alisphenoid and orbitosphenoid bones. Each alisphenoid will

possess a wing shaped structure that projects posteriorly called the pterygoid process. This

process will have a hook-like projection called the pterygoid hammulus. The pterygoid

processes and hammuli help to anchor the soft palate. The supraoccipital and exoccipital will

form the posterior wall. In addition the embryonic ethmoid plate will partially ossify to give rise

to the ethmoid bone. The ethmoid bone and cartilages will house the olfactory bulbs and support

the olfactory mucosa. Ossification areas in the otic capsules will form the petrosal (a.k.a.;

periotic) bones that house the structures of the middle ear. As was the case with Squalus, the

hypophysis rests in the sella turcica. In mammals the sella turcica is a component of the

basisphenoid.

Due to its evolutionary origins the dermatocranium will contribute bones through

intramembranous ossification. In mammals it will contribute paired and unpaired bones. Paired

dermatocranial bones include: premaxillae, maxillae, parietals, malars (a.k.a.; jugals), nasals,

lacrimals, and squamosal bones. Unpaired bones include the frontal and the interparietal. The

temporal complex consists of both endochondral and membrane bones. The squamous bone is of

dermatocranial origin and contributes to the lateral walls of the skull. The tympanic bulla is a

large swelling near the external auditory meatus. It is made up of two components: tympanic

and endotympanic. The tympanic bone surrounds the tympanic membrane and is derived from

the angular bone of the dermatocranium in nonmammals. Near the tympanic bulla is another

portion of the temporal complex called the mastoid. The mastoid is also of dermatocranial origin

and will have a projection called the mastoid process. The temporal complex includes the

endochondrally derives petrous portion. The squamosal portion is the new site of jaw

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Premaxilla Ethmoid Turbinates Malar Orbit Frontal Temporal Fossa Squamosal Parietal Sagittal Crest

Maxilla Perpendicular Plate of Ethmoid Lacrimal Interparietal Supraoccipital Lambdoidal Crest

Felis Skull Dorsal View

Felis Skull Ventral View

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articulation. The remaining bones of the quadrate-articular joint migrate into the ear to become

the auditory ossicles (the articular becomes the malleus and the quadrate becomes the incus).

Felis Skull Ventral View

44

Felis Skull Lateral View

Premaxilla Maxilla Lacrimal Canal Planum Frontal Parietal Squamosal Sagittal Crest

Lacrimal Postorbital Processes Supraoccipital

Canine Premolars Malar Zygomatic Process of Malar External Auditory Canal Tympanic Bulla

Zygomatic Process of Squamosal Mastoid

Felis Skull Lateral View

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Felis Skull, Sagittal Sections

Mammalian skulls have openings within certain bones called cranial sinuses. In Felis the

sinuses are found in the frontal, ethmoid, maxilla, and sphenoid bones. Mammals will have a

primary and secondary palate. Primary palates are found in all vertebrates. The primary

mammalian palate includes an unpaired vomer that makes up part of the nasal septum. The nasal

septum also includes a portion of the ethmoid, mesethmoid, and cartilage. The secondary palate

46

is found only in amniotes. It is a complete palate in mammals and includes the palatine, the

maxillae, and the pterygoid processes of the sphenoids.

In humans the number of bones in the skull has been reduced when compared to that of

the cat. The basioccipital and exoccipitals form the occipital bone. The basisphenoid,

presphenoid, alisphenoids, and orbitosphenoids all join to form the sphenoid bone. The

squamous, mastoid, and petrous form the temporal bone.

Felis Skull, Sagittal Sections

All mammal skulls are synapsid. Synapsid skulls will have an opening on each side

called the temporal fossa. This serves as an anchoring point for the muscles that close the jaw.

Under the temporal fossa will be a bridge-like structure called the zygomatic arch. The

zygomatic arch is formed by the zygomatic process of the malar joining with the zygomatic

process of the squamosal.

The skull of Felis has numerous openings. The openings of the skull typically allow for

the passage of nerves and/or blood vessels. (For example, the hypoglossal canal allows for the

passage of cranial nerve 12, the hypoglossal nerve.) A number of these openings are located in

or near the orbit and include: the lacrimal canal, orbital fissure, infraorbital foramen, optic

canal/foramen, foramen rotundum, and foramen ovale. Others are found on the ventral aspect of

the skull such as the carotid canal/foramen, jugular foramen, hypoglossal canal/foramen, anterior

palatine foramen, posterior palatine foramen, and stylomastoid foramen. The external acoustic

canal is located at the tympanic bulla. The foramen magnum is located on the posterior aspect of

the skull. A few foramina are internal structures such as the internal acoustic canal and olfactory

foramina of the cribriform plate.

An interesting internal aspect of the feline skull is the tentorium. This bony partition

serves to separate the cerebrum from the cerebellum. You will also notice that these bones

47

making up the inner aspect of the cranium will have the impression of cerebral blood vessels and

of the cortex.

Felis Skull Showing a Close Up of Some Foramina

The splanchnocranium of Felis includes the jaws, the hyoid, and some of the

laryngeal cartilages. The upper jaw is incorporated into the premaxillae and maxillae. The

lower jaw has become one bone (actually two that join to form one bone during development),

the dentary or mandible. This represents a reduction in the number of bones making up the

lower jaw when compared to Necturus or to a reptile. Over evolutionary time the size of the

muscles of mastication became larger. This required more room to anchor on to the lower jaw, in

particular the dentary component of the lower jaw. As a result, the dentary became larger and

the other bones of the reptilian lower jaw were reduced in size. Some bones were lost and others

developed new roles. The articular and quadrate bones of the reptilian jaw joint are two of the

three auditory ossicles in mammals. In mammals the lower jaw articulates at the temporal bone

by means of the mandibular condyle. The mandible has a masseteric fossa and coronoid process

on each side to allow for muscle attachment.

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Felis Mandible

Felis Mandible

The hyoid apparatus of Felis is a delicate bony structure that is often lost from articulated

skeletal specimens. It is composed of 11 bones, 5 paired and 1 unpaired. There is a central,

singular basihyal. It is located immediately superior to, and superficial to, the larynx. Extending

posteriorly from the basihyal are the paired thyrohyals. The thyrohyal bones will be on either

side of the thyroid cartilage of the larynx. The remaining hyoid components extend cranially

from the basihyal. The first pair to come off of the basihyal is the ceratohyals. The thyrohyals

are attached to the ceratohyals and are near the angle of the mandible. The stylohyals arise from

the thyrohyals and extend posteriorly to lie near the mastoid bones. In humans the stylohyal will

break off of the hyoid apparatus and attach to the temporal bone to form the styloid process. The

49

tympanohyals arise from the stylohyals and extend posteriorly. They are located near the

tympanic bulla.

Thyrohyal Basihyal Ceratohyal

Thyrohyal Ceratohyal Epihyal Stylohyal

Felis Hyoid Apparatus, posterior view (damaged)

Chapter 1: Skeletal Structure

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Part C: The Appendicular Skeleton

Topic C1: The Pectoral Girdle and Appendage

Both the pectoral limb and girdle are entirely cartilaginous in sharks. The pectoral limb

of Squalus is the pectoral fin. The pectoral girdle consists of the coracoid bar (composed of a

two coracoid cartilages), the paired scapulae, and the paired suprascapulae. The scapula has the

point of articulation between the pectoral fin and girdle called the glenoid. The proximal

cartilages of the pectoral fin are the basalia. There are three basalia per fin. Anteriormost is the

propterygium, then the middle basalia is the mesopterygium, and the posterior element is the

metapterygium. Two rows of radial cartilages attach to the basal cartilages. Anchored into the

distal row of radialia are the numerous ceratotrichia.

The tetrapod pectoral limb and girdle evolved from the pectoral fin and girdle. The

Ceratotrichia Radial Cartilages Metapterygium Suprascapular Cartilage

Mesopterygium Propterygium Glenoid Surface Scapula Coracoid Bar

Squalus Pectoral Girdle

basalia were rearranged with one bone being proximal and the other two becoming paired and

more distal. The proximal basalia became the humerus. The paired distal basalia became the

radius and ulna. The radialia became the carpal bones. Although the evolution of the pectoral

limb is well documented by the fossil record, the origin of the digits is still under some debate.

The basic pectoral girdle developed in Devonian Period fishes and has been modified by

subsequent vertebrates. These primitive fishes had pectoral girdles composed of 7 paired

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elements. Three pairs are endochondral bones of the endoskeleton. These were the suprascapula,

scapula, and coracoid. Four pairs are membrane bones derived from the ancestral dermal armor.

These were the postemporal, supracleithrum, cleithrum, and clavicle. Since chondrichthyes are

cartilaginous, the pectoral girdle of Squalus consists only of the endochondral component. Over

time the number of components to the tetrapod pectoral girdle were reduced. The suprascapular

bones of the endochondral component were lost in bony fishes and most tetrapods. In tetrapods

the intramembranous component has mostly been lost leaving only the clavicle. A new

membrane bone developed in amphibians, the interclavicle. The interclavicle has been retained

in most vertebrates including many reptiles, birds, and monotreme mammals. The scapula is

maintained in all limbed tetrapods since it has the glenoid, the point of articulation between the

humerus and pectoral girdle. Both the clavicle and coracoid brace the pectoral girdle against the

ribcage. As a result, over evolutionary time, one has been lost and the other has been maintained.

Modern amphibians and reptiles possess a coracoid but lack a clavicle. In birds the clavicles have

been maintained and the coracoids have been lost. In mammals the clavicles have become the

dominant bracing bone. The coracoids have been reduced to small projections of the scapula.

The pectoral girdle of Necturus is composed of both bone and hyaline cartilage. There is

a pair of cartilaginous coracoids. These coracoids are ventrally oriented. Extending cranially

from the coraocoids are the long, slender procoracoids. The dorsal component of the pectoral

girdle is the paired scapula and suprascapula. The scapula will have both a bony and

cartilaginous component. The glenoid is on the cartilage component. The suprascapula is a thin

piece of cartilage and is attached to the bony component of the scapula.

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Necturus Pectoral Girdle and Limb (both are from the right side of the body)

The pectoral limb includes a humerus, radius, ulna, carpal bones, metacarpal bones, and

the phalanges. The humerus is the bone of the “arm” in Necturus. The radius and ulna are

paired bones of the “forearm”. They do not show as many distinguishing features in amphibians

as they do in mammals and may be hard to tell apart. There are differences. The proximal

epiphysis of the ulna is the larger epiphysis to articulate with the humerus while the distal

epiphysis of the radius is the larger to articulate with the carpals. The carpal bones are small

short bones arranged into two rows to support the metacarpus. There are four metacarpal bones

to support the four digits. The digits, or phalanges, are composed of three phalanx bones each:

proximal, middle, and distal.

Felis Clavicle

The pectoral girdle of Felis consists of the scapula and a very reduced clavicle. The size

of the clavicle in mammals corresponds to the degree that it is required for locomotion. In bats

and moles they are large while in cetaceans they are lost. In cats the clavicle’s role has been

replaced by the pectoral musculature. The pectoral musculature forms a sling that supports the

pectoral limb. As a result, the clavicle of Felis is fairly small and easily lost. Many students will

not even notice it when they are dissecting the cat. The scapula is a flat bone possessing a

number of projections for anchoring muscle including the coracoid process, acromion, and spine.

It has three depressed surfaces. Dorsally there are the supraspinous fossa and infraspinous fossa.

Ventrally there is the subscapular fossa.

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Felis Scapula

The arm has one bone (each), the humerus. The humerus is a long bone and has the

features typical to that class of bone organ. The proximal epiphysis is rounded to allow for

rotational movement and is called the “head”. The humerus has a number of points for muscle

attachment including the greater tubercle, lesser tubercle, deltoid ridge, pectoral ridge/crest,

epicondyles, and supracondylar crests. Between the greater and lesser tubercle is the

intertubercular/biccipital groove. One of the two tendons of the biceps brachii runs through this

groove. The distal epiphysis is expanded to allow for greater articulation giving the lateral and

medial condyles. The condylar surfaces are shaped to better articulate with the radius and ulna.

The surface for the ulna is the trochlea; a spool-shaped surface that allows for the hinge-like

movement of the humerus-ulna. The surface for the radius is the capitulum; a rounded surface

that allows for the rotational movements of the radius. The radius-capitulum articulation actually

represents a ball-and-socket joint.

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Felis Humerus

The forearm is composed of two bones, the radius and ulna that are parallel to each other.

Running the length of their diaphyses, on their opposing surfaces are the interosseous crests.

The interosseous crest anchors the interosseous ligament which helps to maintain the proper

alignment between these bones. The ulna will articulate with the humerus at the trochlea. It will

have a notch that the trochlea fits into called the semilunar, ulnar, or trochlear notch. The

trochlear notch is found between two processes, the coronoid process and the olecranon. The

olecranon is an anchoring point for the triceps brachii. Distally the ulna narrows and will have a

spike-like process called the styloid process. The radius is wider distally to support the first row

of carpal bones. It will also have a styloid process on its distal epiphysis. The proximal epiphysis

will articulate with both the humerus (at the capitulum) and the ulna (at the radial notch).

Styloid Process Shaft Coronoid Process Trochlear Notch Olecranon

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Radial Notch (on coronoid process) Interosseous Crest Distal Epiphysis

Felis Ulna

(Top Ulna-Right, lateral view Bottom Ulna-Right, Medial View)

L. Radius, Ventral Radial Tuberosity Interosseous Crest Distal Epiphysis Styloid Process

R. Radius, Dorsal Fovea for Capitulum Diaphysis Distal Epiphysis Styloid Process

Felis Radius

The carpus is composed of 7 bones arranged into two rows. The proximal row is

composed of the scapholunar on the radial side, the triquetrum on the ulnar side, and the

pisiform. The scapholunar is actually two fused carpal bones, the scaphoid and lunate as is seen

in humans. The distal row is made up of the trapezium (on the radial side), trapezoid, capitate,

and hamate (on the ulnar side). The metacarpus is composed of five bones numbered first

through fifth from the dewclaw side. Typically there are five digits. All but the first are

composed of three bones: proximal phalanx, middle phalanx, and distal phalanx that has the

claw. The dewclaw has only two phalanx bones, the proximal and distal, and as a result a special

name is given to this digit: pollex.

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Felis Right Forefoot, Dorsal View

Topic C2: The Pelvic Girdle and Appendage

The pelvic fin and girdle of Squalus are composed of cartilage. While the structure of the

pelvic fin is similar to that of the pectoral fin, the girdles have some notable differences. The

pelvic girdle in fishes is poorly developed and is not as closely associated with the vertebral

column as is the pectoral. The pelvic girdle of Squalus consists of an ischiopubic bar. The

ischiopubic bar will have small, lateral projections called iliac tubercles/processes and the

articulating surface of the pelvis, the acetabulum. The pelvic fin has only two basalia, the

propterygium and the metapterygium. The propterygium is small and can be misidentified as a

radial cartilage. The metapterygium is large and will support a single row of radial cartilages

Acetabular Surface Ischiopubic Bar Iliac Process Propterygium

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Ceratotrichia Radial Cartilages Clasper Cartilage Metapterygium

Squalus Male Pelvic Girdle

Acetabular Surface Ischiopubic Bar Iliac Process Propterygium

Ceratotrichia Radial Cartilages Metapterygium

Squalus Female Pelvic Girdle

which in turn support the ceratotrichia. The metapterygium will support the clasper cartilages in

male chondrichthyes. The claspers are the intromittent organs in these fishes.

Sacrum Sacral Rib Ilium

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Pubis Puboischiadic Plate Ischium

Necturus Pelvis

The pelvic girdle of Necturus consists of both bone and cartilage. Tetrapod pelvic girdles

will begin as cartilage but tend to ossify during development. The greater strength of bone

allows the pelvis to withstand the pressure that it will be exposed to during life. However, since

Necturus is aquatic, the pelvis of this species is not exposed to the amount of mechanical stress

typical for a tetrapod. There are three paired components to a tetrapod pelvic girdle: the ilium,

ischium, and pubis. The ilium will articulate with the sacrum. Collectively these three pairs of

skeletal structures will have the joint cavity, the acetabulum. The combination of the pelvic

girdle and sacrum forms the structure known as the pelvis. In Necturus the ilium is a slender

bone that articulates with the sacrum by means of a sacral rib. The pubis is cranial and the

ischium is caudal relative to one another. The pubis is composed of cartilage and will be pointed

in Necturus. The ischia are composed of both cartilage and bone. The pubis and ischial

cartilages will grow together during development to form the puboischiadic plate. The

puboischiadic plate will have a pair of openings called the obturator foramen for passage of the

obturator nerve.

The thigh of Necturus has the femur, which articulates at the acetabulum of the pelvic

girdle. The tibia and fibula are the paired bones of the leg. As is the case with the radius and

ulna these paired bones each possess an interosseous margin to anchor the interosseous ligament.

The two bones are similar in size and appearance. The fibula is the laterally oriented bone. The

tarsal bones are small short bones that support four metatarsals. The four metatarsals support

four phalanges composed of three phalanx bones each

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Necturus Pelvic Girdle and Limb

Felis Os Coxa

The pelvic girdle of Felis is composed of the paired hip bones and the sacrum. The hip

bone is called the os coxa or innominate and is made up of three fused bones: the ilium, ischium,

and pubis. The two os coxae articulate with the sacrum to form the pelvis. The os coax has a

60

large opening called the obturator foramen that decreases the weight of the pelvis and allows for

passage of the obturator nerve. The ilium is the dorsal bone of the os coxa. The ischium and

pubis are ventral relative to the ilium. The pubis is cranial and the ischium is caudal.

Felis Femur

The thigh is composed of one long bone, the femur. The femur, like the humerus, as a

rounded portion to the proximal epiphysis termed a “head”. As is typical of the appendicular

skeleton, the femur has many points of muscular attachment including: the greater trochanter,

lesser trochanter, intertrochanteric crest, gluteal tuberosity, linea aspera, lateral and medial

epicondyles, and popliteal surface. The distal epiphysis is expanded, giving rise to the lateral and

medial condyles, to allow for greater articulation with the leg. Anteriorly the distal epiphysis has

a roughened point for attachment of the patellar tendon called the patellar surface. This allows

for attachment of a sesamoid bone called the patella. The patella reinforces the knee joint.

The leg is composed of two bones, the tibia and fibula that are parallel to each other. Running

the length of their diaphyses, on their opposing surfaces are the interosseous margins. The

interosseous margin anchors the interosseous ligament that helps to maintain the proper

alignment between these bones. The tibia is the weight bearing bone of the leg and will articulate

with the femur. To facilitate this the tibia will have well developed condyles. Near the condyles

will be a roughened elevation, the tibial tuberosity, which anchors the patellar tendon. The distal

epiphysis of the tibia has a flattened process called the medial malleolus. In mammals the fibula

is much more slender than the tibia. The proximal epiphysis will have a styloid process and the

distal epiphysis will have the lateral malleolus.

61

apex

Felis Patella

Felis Tibia

Styloid Process L. Fibula Medial View Interosseous Margin Distal Epiphysis

Lateral Malleolus Peroneal Groove L. Fibula Lateral View Head of Fibula Styloid Process

Felis Fibula

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The hind foot of Felis is composed of the tarsals, metatarsals, and phalanx bones. There

are seven tarsal bones arranged into three rows. The proximal row contains the talus and the

calcaneus. The talus articulates with the tibia and the calcaneus articulates with the fibula and

talus. The middle row is composed of one short bone, the navicular. The distal row is composed

of four bones. There are three cuneiforms and they articulate with the navicular. They are

named the medial, intermediate, and lateral cuneiforms. Each cuneiform supports one metatarsal.

Lateral to the lateral cuneiform is the cuboid. The cuboid supports the fourth metatarsal. Felis

has four metatarsals bones in the pes. They are numbered one through four counting medial to

lateral. Each metatarsal supports one phalange that is composed of three phalanx bones.

Distal Phalanx Middle Phalanx Proximal Phalanx Metatarsal Cuboid Calcaneus

Lateral Cuneiform Intermediate Cuneiform Medial Cuneiform Navicular Talus

Felis Hind Foot Dorsal View

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Chapter 2: Myology

Part A: An Introduction

Myology is a study of muscles; muscle cells, muscle tissue, and muscle organs. In this

chapter we will be focusing on skeletal muscle organs. Skeletal muscle organs are composed

primarily of skeletal muscle tissue but also include blood vessels, nerves, and connective tissue

sheaths. There are three connective tissue sheaths associated with skeletal muscle organs. A

muscle cell will be elongated. This allows the muscle to contract, to shorten its length causing it

to pull on a bone and produce a movement. As a result, a muscle cells is called a myofiber or

fiber. Each myofiber in a skeletal muscle organ will be ensheathed by a thin connective tissue

membrane called the endomysium. Groups of endomysium encased myofibers form an

organizational unit called a fascicle. The fascicle will be covered in another connective tissue

sheath called the perimysium. Groups of fascicles will form a skeletal muscle organ. A tough

connective tissue sheath called the epimysium will cover the organ. The epimysium is rich in

collagen bundles. During development it will extend from the muscle to meet with extensions

from the periosteum of a bone to form a tendon. The epimysium is sometimes referred to as

“deep fascia”.

In this chapter you will be required to learn a number of skeletal muscle organs, their

attachments, and their actions. Skeletal muscles are termed “skeletal muscles” because they

typically attach to the skeleton. This attachment will be either direct (by the epimysium fusing to

the periosteum) or indirect (by means of a tendon or aponeurosis). The two attachments are

termed origin and insertion. The origin is the attachment that does not move when the muscle is

contracted. The insertion is the attachment that does move when the muscle contracts. When

learning skeletal muscles you may find it to be more efficient to identify the muscle, follow it to

its origin and insertion, and then think of the movement that it’s contraction will cause. This

should allow you to learn this material faster and to retain it longer. Also. it also helps to match

up these muscles to your own body and to actually exercise the muscle a few times to feel out the

origin, insertion, and action.

It is useful to review how skeletal muscles are named prior to attempting to learn them.

Many of the muscles that we will study follow these rules and, once you understand these rules,

their names should be relatively easy for you to learn. Sometimes more than one of these criteria

will be used to name the muscle:

(1) Location - some names describe the location of the muscle.(ex; the intercostal

muscles are located between the ribs)

(2) Shape - some names describe the shape of the muscle (ex; deltoid, trapezius).

(3) Size - some names describe the size of the muscle relative to other muscles (ex;

major, minor, maximus, minimus, longus, brevis).

(4) Direction - some names describe the direction in which the muscle’s fibers

run. Muscle “fibers” refers to muscle fascicles, not muscle cells. Fascicle patterns are

visible. Different arrangements of fascicles are classified and reflected in muscle

shapes and functions:

(a) Parallel - the long axis of the fascicles run parallel to the long axis of

the muscle (ex; biceps brachii). Although the fibers are running parallel to

the long axis of the muscle, the muscle may or may not be parallel to the midline

of the body. This results in different types of parallel fiber patterns:

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[1] Rectus (meaning “straight”) - the fibers are running parallel to the body

midline (ex; rectus abdominis)

[2] Oblique - the fibers run obliquely to the body midline (ex; external

abdominal oblique).

[3] Transverse - the fibers are running at a right angle/perpendicular to the

body midline (ex; transversus abdominis).

(b) Pennate - the fascicles are short and attach obliquely to a tendon which runs the

length of the muscle. There are three types:

[1] Unipennate - the fascicles only attach to one side of the tendon (ex;

extensor digitorum longus).

[2] Bipennate - the fascicles attach to two sides of the tendon (ex; soleus ).

[3] Multipennate - the fascicles attach to more than two sides of the tendon (ex;

deltoid).

(c) Convergent - the origin of the muscle is broad and the muscle narrows as it

approaches the insertion (ex; pectoralis major).

(d) Circular/Sphincter - the fascicles are arranged in concentric rings (ex;

orbicularis oculi).

: (5) Location of Origin and/or Insertion – in this case the muscle is named for the

bone or bones that it is attached to. When both the origin and the insertion are present

in the name of a muscle, the origin name usually comes first (ex.; brachioradialis,

sternomastoid).

(6) Action - the muscles are named for the action which they produce (ex; the

supinator supinates the forearm). Many times the region of the body

that the muscle is located in will help you to remember it’s action. For example the

muscles of the dorsal aspect of the limbs are generally extensors and those of the

ventral aspect of the limbs are typically flexors.

(a) Types of Movements

[1] Extensors - increase the angle between two bones

[2] Flexors – decrease the angle between two bones.

[3] Abductors – move a limb away from the midline of the body

[4] Adductors – move a limb towards the midline of the body

[5] Protractors – thrust a part of the body forward (ex; mandible,

or tongue)

[6] Retractors – pull a part of the body back

[7] Levators – raise a structure of the body

[8] Depressors – lower a structure of the body

[9] Rotators – rotate a body part on its axis

[10] Supinators – rotate the palm/sole upwards

[11] Pronators – rotate the palm/sole downwards

[12] Tensors – increase the tension on a structure

[13] Sphincters – decrease the size of an opening.

[14] Dilators – increase the size of an opening.

You should also remember that the muscles were first named in humans. When muscles

were identified in other species that had the same basic origin and insertion they were given the

65

same name as they have in humans. However, humans being bipedal have some unique

myological features. For example: only in hominids is the gluteus maximus the largest gluteal

muscle to power our unusual mode of locomotion. More typically the gluteus medius is larger

than the gluteus maximus. However, due to the rules of muscle nomenclature, the smaller

gluteus maximus is still called the “maximus”.

Skeletal muscle organs can be divided up into axial muscles and appendicular muscles.

Axial muscles are the skeletal muscles of the trunk and tail. They run from the tail to beneath the

pharynx. In all vertebrates axial muscles will display metamerism, a primitive, but retained,

characteristic. The metameric axial muscles combined with flexible metameric vertebral column

allows for locomotion in fishes, some aquatic tetrapods, and limbless terrestrial tetrapods. Axial

muscles are metameric because of their origin from segmental mesodermal somites. This

metameric pattern is especially visible in fishes where the axial muscles are arranged into

segments called myomeres separated by tendinous myosepta (a.k.a.; myocommata).

Appendicular muscles are the muscles of the limbs and their associated girdles. Since most

fishes use axial muscles for locomotion, appendicular muscles in fish are of a limited function.

As a result they are low in number and variety, are uncomplicated, and have little mass. The

appendicular muscles of tetrapods have become increasingly numerous and complex as a result

of the needs of terrestrial life. Correspondingly the role of axial muscles has been reduced in

tetrapods

Skeletal muscle organs can either work together (synergistic) or against one another

(antagonistic) to perform a task. In an antagonistic muscle interaction two (or more) muscles

produce opposite movements on a structure. One muscle will be termed the “agonist” and the

other will be termed the “antagonist”. The agonist or prime mover produces a particular

movement (ex; the biceps brachii causes flexion of the forearm). The antagonist opposes or

reverses the movement of the agonist (ex; the triceps brachii causes extension of the forearm).

When the agonist is acting the antagonist is either at rest or only slightly contracted so as to

control the extent of motion produced by the agonist. The antagonist can also be the agonist for

another motion and in that case it is the previous agonist that acts as the antagonist. For example:

if instead of forearm flexion, we are discussing forearm extension the triceps brachii would be

the agonist and the biceps brachii would be the antagonist.

Most movements will also involve one or more muscles that assist the prime mover.

These muscles are termed synergists. Synergists work either by adding force to a movement or

by reducing undesirable extra movements (ex; the quadriceps group is composed of the vastus

lateralis, vastus medialis, vastus intermedius, and rectus femoris. All four muscles work together

to extend the leg.

In this lab we will be studying two types of skeletal muscle organs: somatic and

branchiomeric muscles. Somatic muscles are those muscle organs that control the “soma”, the

body. All somatic muscle organs are composed of skeletal muscle tissue. Typically they are

innervated by branches of spinal nerves (the exception is a few of the tongue muscles) and are

voluntary (however reflex contractions will occur). Somatic muscles are derivatives from

myotomes of mesodermal somites. As a result somatic muscles are sometimes also referred to as

myotomal or somitic muscles. Branchiomeric muscle organs (a.k.a.; pharyngeal arch muscle

organs) are also composed of skeletal muscle tissue. Branchiomeric somatic muscle organs are

the muscles of the pharyngeal arches and their ontogenetic and phylogenetic derivatives. Like

somatic muscle organs, branchiomeric somatic muscle organs are derived from myotomes.

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However, they are derived from the anteriormost somites and the unsegmented paraxial

mesoderm in the head. Paraxial mesoderm shows incomplete segmentation. Individual

subdivisions are termed somitomeres. Somitomeres differ from somites in that they are not fully

segmented and lack some of the components found in somites. As a result, these muscle organs

are also referred to as somitomeric muscles. They are innervated by cranial nerves instead of

spinal nerves. Their innervation also differs from that of the typical skeletal muscle tissue in that

there is both a voluntary and an involuntary aspect of control. The voluntary control that you

have over swallowing is due to a branchiomeric muscle in your esophagus. The involuntary

aspect of this muscle includes the “gag” reflex.

Chapter 2: Myology

Part B: Muscle Dissection Techniques

Muscle dissection takes patience and good technique to provide the student with a

specimen that clearly demonstrates the structures to be examined. For the effective study of

muscle organs it is essential that you have a good anatomical specimen.

You will be dissecting both superficial and deep muscles. Superficial muscles are located

close to the integument. They will be exposed by carefully removing the skin and fascia. Fascia

is a general term for the hypodermis and epimysium covering a muscle organ. The hypodermis

is referred to as “superficial fascia” and the epimysium is referred to as “deep fascia”. The

degree of difficulty involved in removing the fascia will be based on a number of factors such as

the age of the animal (the deep fascia is tougher in older animals) and the amount of fat on the

animal. We want to remove most of the epimysium to make it easier to see the “fiber pattern” of

a muscle organ. The fiber pattern is actually the pattern of the fascicles in a muscle organ.

When they are exposed they can often tell a student how the muscle will act. To a lesser extent

the fascicle pattern will also make it easier to see the attachments of the muscle to the skeleton.

The best strategy is to do one side of the animal at a time. That way if an error is made you will

be aware of a potential problem when you perform the same dissection on the other side. The

entire animal should be dissected superficially first, on both sides. Once you have completed the

superficial dissection evaluate your performance. The side with the greatest number of errors

should be your deep side.

In the deep dissection you will be exposing the muscles that lay beneath the superficial

muscles. This is done by “cutting and reflecting” the superficial muscle. If the muscle’s origin

and insertion are intact, you cut the belly of the muscle width-wise and then fold the two cut

halves back to the origin and insertion (called “reflecting”). Because of this approach the impact

of many of the mistakes that you made during the superficial muscle dissection will be reduced.

The technique to expose the muscles in a superficial dissection is called the “pressing

technique”. Utilizing the scalpel and micro-tooth tissue forceps you will press the skin away

from the hypodermis and the fascia away from the muscle. Of the three animals that we are

studying Felis is the most convenient to practice the pressing technique on. Mammals have a

well-defined hypodermis which will give you a margin of error as you become comfortable with

this technique. Squalus has the collagenous component of the dermis anchoring directly on to

the epimysia and the skin is difficult to get through due to its numerous denticles. Necturus has

fairly thin skin that also anchors on to the epimysia of its muscles in many places. Necturus is

67

also a good deal smaller than the other two specimens which will magnify the effects of any

slight mistake.

The first thing that you need to familiarize yourself with is how to hold the scalpel. You

should be working with a metal scalpel handle. Plastic handles do not afford the stability for

precise dissections. The scalpel handle has roughened portion behind the blade. Rest the scalpel

handle against your middle finger at the roughened portion. Your thumb should be placed on the

opposite side, also at the roughened portion, and slightly behind the location of your middle

finger. This way the handle is gripped between your middle finger and thumb. Your index finger

should be placed on the edge of the handle between your middle finger and thumb. The index

finger will act as a guide for the blade while dissecting. This gives you a more precise grip

resulting in a higher degree of control when working with the scalpel. The blade will be

controlled by your fingertips. The movement of your scalpel hand is more like the painting of a

portrait than the slicing of meat.

When removing the integument you will first be removing the dermis from the

hypodermis. The blade should be positioned so that the cutting edge is at a 45o angle from the

hypodermis. The edge will be pointed towards the dermis in the direction of movement of the

scalpel. This will seem odd to you at first. You would expect to have the blade facing the

hypodermis. However, if you were to hold the blade that way and made a mistake, you would

slice into the hypodermis which we are trying to preserve for practice purposes. If you are

holding the scalpel correctly and make a mistake you are more likely to slice into the skin which

you are removing and are not concerned about. What allows this technique to work is tension.

While you are moving the scalpel you will be pulling on the skin with the micro-tooth tissue

forceps. This will stretch and strain collagen bundles that anchor the skin to the hypodermis

making it easier for the blade to slice through them and remove the skin. You will be able to see

these collagen bundles with the unaided eye as you work to remove layers from above the

muscles. The key is to maintain tension by moving the forceps hand along with the scalpel hand.

(It is easy to forget to keep the forceps hand moving and, once the tension is reduced, you will

most likely slice into the abovelying skin.) You will actually feel more fatigue with your forceps

hand than with your scalpel hand by the end of the lab period. You should work the scalpel along

a lane. Once you come to the end of the lane it is time to start a new one. However, you do not

want to pick up the blade from the animal and move it a new location; that increases the chances

of making a mistake. Instead keep the scalpel where it is and rotate it 90o. Now the blade is

facing in the opposite direction and you can make a second lane, overlapping with the first.

Repeat this again and again until you have removed the skin.

When working on the fascia you should remove one layer at a time using the pressing

technique. This is tedious but necessary to avoid damaging the muscles that you wish to study.

Remove the hypodermis first but be careful. The integument of Felis contains cutaneous skeletal

muscle fascicles that make up the muscle of the integument, the cutaneous maximus. The

cutaneous maximus looks a bit like the muscles that you are trying to save and will fuse on to

some of those muscles in certain locations. You should first remove the portion of the

hypodermis superficial to these muscle fibers so that you can observe them and safely remove

them from your specimen. Another difficulty is that there are a number of superficial blood

vessels and structures that you will wish to preserve (ex; radial artery, vein, and nerve and the

brachioradialis of the forearm). These will often be partially concealed in adipose of the

hypodermis. The fatter the animal the more likely it is that you will lose structures by

68

injudiciously removing the adipose. For working in fatty areas it is better to use another

technique, the “separating technique”.

In the separating technique you utilize your fine-point dissection scissors instead on your

scalpel. Place the closed scissors into the fat and gently open the blades. This will cause the fat

to fragment without damaging other structures. Close the blades before you move the scissors to

another location and repeat. The fat will break up and expose the structures that you are trying to

save. As with the scalpel you want to hold the fine-point dissection scissors in a grip that will

allow you to be as precise as possible. There are two grips that work well, although the first one

is a little better than is the second. The first grip is to place your thumb and ring finger into the

rings of the scissors handle. Rest the weight of the scissors on the middle finger and place the tip

of your index finger against the screw holding the two blades together. This will decrease the

shaking of the blades and allow for more precision as you work the scissors. The degree of

shaking may seem minimal but you will be trying to observe some small structures that can be

easily damaged. The second grip is to place your thumb and middle finger into the rings of the

scissors handle. The index finger can either be placed against the screw holding the blades

together or you can rest the scissors on the index finger. This grip is not quite as precise as the

first one but is more stable than the grip that you are used to using.

Once you have removed the hypodermis you will move on to the deep fascia, the

epimysium. This part of the dissection will require patience. It can take a bit of time to remove

this layer but it is worth it. Again you will be using the pressing technique and, since you are

very close to the muscle that you wish to preserve, you will need to be very careful with your

technique.

Demonstration of the Proper Grip for Holding the Fine-point Dissection Scissors

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Demonstration of the Proper Grip for Holding the Scalpel

Making the Initial Incision

Note: The scalpel is held at a 45o angle to the underlying muscle, pointed in the direction of the

cut and facing away from the muscle that you wish to save.

70

Expanding the Incision

The tension on the collagen fibers from the fine-tooth tissue forceps makes it easier to slice through them.

As you “hit” the edges of the incision you will expand the incision.

Reversing Direction

Once you have completed one “lane” using the pressing technique you reverse direction to start a new

lane. Rotate the blade 90o. Now you are ready to work in the opposite direction.

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The Pressing Technique

Notice how the collagen bundles are straining due to the forceps allowing the scalpel to more

easily cleave through them.

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Chapter 2: Myology

Part C: The Muscles

Topic C1: The Muscles of Squalus

In fishes axial muscles are the predominant muscles of locomotion. The muscles of the

fins play a minor role in locomotion, typically steering or stabilizing the thrust produced by the

axial muscles. As a result the appendicular muscles of fishes in general, and of Squalus in

particular, will be of limited size, diversity, and function.

The first step in the muscle dissection of Squalus is to remove the skin using the pressing

technique. The collagen of the dermis anchors on to the collagen of the epimysium in Squalus.

As a result you will be able to see the muscles as soon as you remove the skin. Many times the

muscle will begin to fray as you are pressing away the skin. You should increase tension with

the forceps hand to decrease the amount of fraying. Some areas will be very difficult to remove

the skin from without damaging underlying structures. The skin around the gills is a good

example of that. You will need to remove the skin from the base of the chondrocranium to the

base of the first dorsal fin dorsally and from the Meckel’s cartilage to the point opposite the first

dorsal fin ventrally. You will also need to remove the skin from the base of the pectoral fins,

both dorsally and ventrally. There will typically be one layer of fascia left to remove after the

animal has been skinned. This fascia will be tightly attached to the muscle and will require

patience to remove.

The muscles of the body wall and tail in fishes such as Squalus consist of myomeres

separated by myosepta into which the longitudinally arranged muscle cells attach. These muscles

are well developed being the muscles for locomotion. The myomeres have a “zigzag” pattern

immediately beneath the skin. The segmental arrangement of the axial muscles is easy to

observe in Squalus. There is one myomere per vertebra and one spinal nerve per myomere. As is

true for all fishes other than agnathans, the myomeres of Squalus are divided into dorsal and

ventral masses. The dorsal and ventral muscle masses are the epaxial and hypaxial muscles

respectively. A sheet of tendinous material called the horizontal skeletogenous septum separates

the epaxial and hypaxial muscles. The horizontal skeletogenous septum stretches between the

vertebral column and the skin along the entire trunk and tail. It will also anchor on to the dorsal

ribs of Squalus. The muscles of the pectoral and pelvic girdles interrupt the metameric

arrangement of myomeres. These girdles interrupt only the hypaxial muscle segmentation. The

epaxial muscles are dorsal to the girdles and as a result will not be affected. The epaxial muscles

will extend cranially on to the skull. Those epaxial muscles located dorsal to the gills are termed

epibranchial muscles. Those hypaxial muscles located ventral to the gills are termed

hypobranchial muscles. The innervation of the epaxial and hypaxial muscles is also metameric.

Epaxial muscles are innervated by the dorsal rami of spinal nerves. Hypaxial muscles are

innervated by the ventral rami of spinal nerves. This pattern of innervation is seen tetrapods as

well.

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Epibranchial Muscles Horizontal Septum Myomere Myoseptum Epaxial Muscles

Branchiomeric Muscles Hypaxial Muscles

(disrupted segmental pattern due to pectoral girdle)

Squalus Muscles Showing the Relationship of Epaxial and Hypaxial Muscles

The hypobranchial muscles can be seen on the ventral surface of Squalus. They are

located between the pectoral girdle and Meckel’s cartilage. The hypobranchial muscles will be

closely associated with the branchiomeric muscles. To observe them you will need to cut and

reflect the intermandibularis. This can be done removing the right or left muscle at the

midventral raphe and then folding it to the Meckel’s cartilage .The hypobranchial muscles are:

common coracoarcurals (2), coracomandibular (1), coracohyoids (2), and the coracobranchials

(10).

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Squalus Muscles, Ventral View:

Deep Hypaxial, Hypobranchial, Branchiomeric, and Ventral Appendicular Muscles

(*Note the difference in the fiber pattern between the interhyoid and intermandibular)

The Branchiomeric Muscles

Muscle Origin Insertion Action

First Ventral Constrictor (Intermandibular) Mid-ventral Raphe Meckel's cartilage Raise the floor of the mouth

Second Ventral Constrictor (Interhyoid) Hyomandibula Ceratohyal Compresses oropharynx

Third through Sixth Ventral Constrictors Vertical Raphe Vertical Raphe Compresses oropharynx

Coracobranchials Coracoid Bar Ventral Gill Cartilages Expands oropharynx

First Dorsal Constrictor - Spiracular Otic Capsule Palatopterygoquadrate Aids to elevate palatoquadrate

- Mandibular Adductor Palatopterygoquadrate Mandibular Arch Closes mouth

Second Dorsal Constrictor Otic Capsule Hyomandibula Compresses oropharynx

Third through Sixth Dorsal Constrictors Vertical Raphe Vertical Raphe Compresses oropharynx

First Levator (Palatopterygoquadrate

Levator) Otic Capsule Palatopterygoquadrate Elevates palatopterygoquadrate

Second Levator (Hyoid Levator) Epihyoideus Epihyoideus Elevates hyoid

Third through Sixth Levators (Cucullaris) Fascia of Epaxial Muscle Scapula Elevates scapula

Coracomandibular Coracohyoid Common Coracoarcural

Intermandibular

Interhyoid*

Coracomandibular Coracohyoid Common Coracoarcural

Intermandibular

Interhyoid*

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The branchiomeric muscles derive from splanchnic mesoderm (unlike the hypobranchial

muscles that derived from somatic mesoderm). They control the movements of the

splanchnocranium, the jaws and gill arches. They surround the oropharynx and can be observed

ventrally, laterally, and dorsally. The branchiomeric muscles are the dorsal constrictors, the

ventral constrictors, and the levators (all numbered first through sixth). The first dorsal

constrictor is actually two muscles: the spiracular and the mandibular adductor. The mandibular

adductor increased in size and points of attachment during tetrapod evolution and became three

masticatory muscles of mammals: the masseter, temporalis, and pterygoideus. The first ventral

constrictor is also known as the intermandibularis. The intermandibularis gave rise to the

mammalian mylohyoid and possibly the digastric muscles. Immediately deep to it is the second

ventral constrictor, the interhyoideus. It can be observed by cutting and reflecting the

intermandibularis. The interhyoideus can be distinguished from the intermandibularis by its

fiber pattern. The intermandibularis has an oblique pattern while the interhyoid has a transverse

fiber pattern. The first and second levators elevate the palatopterygoquadrate to open the mouth.

The third through sixth levators are also known as the cucullaris. The cucullaris is homologous

to the trapezius of amniotes.

Squalus Muscles, Ventral View:

Superficial Hypaxial, Hypobranchial, Branchiomeric, and Ventral Appendicular Muscles

The Hypobranchial Muscles

Muscle Origin Insertion Action

Common Coracoarcural Coracoid Bar Mandibular Adductor Aids to open mouth

Coracomandibular Coracoid Bar Meckel's Cartilage Opens mouth

Coracohyoid Coracoid Bar Basihyal of Hyoid Braces jaws for feeding

Coracobranchials Coracoid Bar Ventral Gill Cartilages Expands oropharynx

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The appendicular muscles are reduced to levators (extensors) and depressors (flexors) of

the fins. The two observed in this lab are the pectoral levator and the pectoral depressor. During

vertebrate development the long plane of the limb is defined by its skeletal components. This

establishes a dorsal plane and a ventral plane. The mesoderm of the dorsal plane differentiates

into extensor muscles and the mesoderm of the ventral plane differentiates into flexor muscles.

You can observe this pattern in the fins of Squalus and limbs of Necturus and Felis.

Squalus Muscles Dorsal View: Superficial Branchiomeric Muscles

The Appendicular Muscles

Muscle Origin Insertion Action

Pectoral Levator Scapula Pterygiophores Elevate/extend pectoral fin

Pectoral Depressor Coracoid Bar Pterygiophores Depress/flex pectoral fin

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Topic C2: The Muscles of Necturus

In Necturus we have a nice example of the transition between aquatic and terrestrial

existence and its correlation in the musculature. Necturus has retained the primitive metameric

pattern of epaxial and hypaxial muscles seen in fishes. This allows these aquatic urodeles to

swim like fish, utilizing the axial musculature and lateral undulations of the vertebral column.

Amniotes gradually lost much of the metamerism of the axial muscles. The disappearance of the

epaxial myotomes led to the development of long, strap-like or pennate muscle bundles in

amniotes. These changes in muscles correlated with changes that increased the flexibility of the

vertebral column so as to improve the movement of the trunk for life on land. (Think about how

a whale swims versus a shark.) Changes also occurred in the lateral body wall. Broad muscular

sheets arranged in layers gradually replaced the hypaxial muscles. The muscle fascicles of each

sheet are arranged in a different direction than those of neighboring muscle sheets. This fiber

pattern is possible since these muscles are no longer used for locomotion. That role has been

taken over by the appendicular muscles. Instead the muscles of the lateral wall serve to support

the viscera in a “muscular sling”. Intermediary stages in this transition can be observed in extant

species such as Necturus which shows epaxial and hypaxial myomeres. However, the hypaxial

myomeres are arranged into three sheets: external abdominal oblique, internal abdominal

oblique, and transversus abdominis. We see the same three muscle sheets in amniotes such as

Felis.

The appendicular muscles of Necturus are much better developed than are those of fishes

but not as well developed as are those of amniotes. One example of this is the latissimus dorsi.

In urodeles, such as Necturus, it is a thin, triangular muscle originating from the fascia of epaxial

muscle near the shoulder. In amniotes, such as Felis, it is a broad sheet, covering a much larger

area, originating from the transverse processes of cervical, thoracic, and lumbar vertebrae. In

Necturus the origin of the latissimus is so weak that you may remove the muscle when skinning

your specimen. The pattern of tetrapod muscle evolution is an increase in the size, number, and

strength of attachments over time. This can be observed by comparing Felis to Necturus.

The skin of Necturus is thin and care must be taken with its removal. As previously

mentioned, without attention it is easy to remove some muscles including all of the dorsal

pectoral musculature and branchial levators. There is very little hypodermis in amphibians. In

many locations the dermis will be immediately superficial to the muscle. It is best to begin at the

tail. Using the pressing technique you can start by removing the skin from the tail and working

your way cranially. Observe the numerous large glands on the underside of the skin in the tail.

With good technique the skin can be safely removed. When you get to the ventral head you

should change direction, however. You should resume pressing the skin away at the dentary and

work your way caudally. This is to avoid the gular fold, a fold of skin at the posterior aspect of

the lower jaw. It will have some fibers of the interhyoid attached to it. If you were to attempt to

remove it going caudal to cranial you could easily remove the interhyoid and intermandibular

muscles along with the skin. You do not need to change direction while skinning the dorsal

head.

The axial muscles of Necturus display a metameric pattern and demonstrate myomeres

and myosepta. They can be divided into hypaxial and epaxial muscles by the horizontal

skeletogenous septum. The epaxial muscles of the trunk and dorsal gill region are called the

dorsalis trunci. The hypaxial muscles of the trunk are arranged into three broad sheets: external

abdominal oblique, internal abdominal oblique, and transversus abdominis; running superficial to

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deep. The external abdominal oblique has its fibers running at a 45o angle to the midline of the

body. The internal abdominal oblique also has its fibers running at a 45o angle to the midline of

the body but these fibers are perpendicular to those of the external abdominal oblique. The

fibers of the transversus abdominis are perpendicular to the midline of the body as its name

indicates. The right and left muscle sheets do not meet medially. Between them is the rectus

abdominis. These paired muscles meet at the linea alba of the midline and extend from the pubis

to the pectoral region. The rectus abdominis will show regular segmentation with its myomeres

being separated by myosepta, a pattern that we see even in ourselves. The portion of the

hypaxial muscles in the ventral gill region is the rectus cervicis.

The muscles of the head and gill region include hypobranchial, epibranchial, and

branchiomeric muscles. The epibranchial muscles are the cervical portion of the dorsalis trunci.

The hypobranchial muscles include the rectus cervicis and geniohyoid. The rectus cervicis will

have a segmental pattern. However, that metameric pattern is disrupted by cranial elements of

the pectoral girdle. Posterior slips of the rectus cervicis will attach to the procoracoids to give

rise to the omoarcual muscle. With the development of the neck the hypobranchial muscles

became more strap-like as can be seen with the geniohyoid and branchiohyoid. The

branchiomeric muscles have begun to take on other roles although the branchial levators do serve

to move the gills. The mandibular adductor of Squalus has expanded to become the anterior

mandibular adductor, external mandibular adductor, and mandibular depressor of Necturus.

These muscles are homologous to the temporalis, masseter, and (possibly) digastric of mammals

Necturus, Some Axial MusclesThe Axial Muscles of the Trunk

Muscle Origin Insertion Action

Dorsalis Trunci Myosepta & Vertebrae Myosepta & Vertebra Laterally flexes trunk

External Abdominal

Oblique

Myosepta & Horizontal

Septum

Myosepta & Horizontal

Septum Laterally flexes trunk

Internal Abdominal

Oblique

Myosepta & Horizontal

Septum

Myosepta & Horizontal

Septum Laterally flexes trunk

Transversus Abdominis Horizontal Septum Linea Alba Laterally flexes trunk

Rectus Abdominis Puboischiadic Plate Coracoid Ventrally flexes trunk

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Necturus Dorsal Muscles of the Head and Trunk

The Muscles of the Head and Pharyngeal Region

Muscle Origin Insertion Action

Anterior Mandibular

Levator Parietal & Frontal Dentary Raise lower jaw

External Mandibular

Levator Parietal & Frontal Dentary Raise lower jaw

Mandibular Depressor Parietal & Squamosal Angular Depress lower jaw

Dorsalis Trunci Myosepta & Vertebrae Parietal & Opisthotic Laterally turns head

Branchial Levators Fascia of Epibranchials Epihyals Raise gills

Intermandibular Dentary & Angular Median raphe Tenses floor of oropharynx

Interhyoid Fascia of Branchiohyoid Median raphe Tenses floor of oropharynx

Geniohyoid Dentary Second basibranchial Moves hyoid cranially

Branchiohyoid First gill arch Ceratohyoid Moves hyoid cranially

Rectus Cervicis Coracoid Ceratohyoid Moves hyoid cranially

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Necturus Ventral Muscles of the Head and Pharyngeal Region

respectively. As in Squalus the intermandibularis and interhyoid are superficial muscles of the

ventral head. They are distinguished by their fiber patterns and can be separated by lightly using

the separation technique with the tips of your scissors. (To observe the geniohyoid and

branchiohyoid you must cut and reflect the intermandibular and interhyoid.) The

intermandibularis is homologous to the mylohyoid and possibly the anterior portion of the

digastric in mammals.

The appendicular muscles of tetrapods are much more complex and diverse than are

those of fishes. They can be divided up into the muscles of the pectoral girdle and anterior limb

and the muscles of the pelvic girdle and posterior limb. The appendicular muscles are typically

innervated by the ventral rami of the spinal nerves and are under somatic motor control. During

development somatic mesoderm will grow into the limb bud and differentiate into a dorsal mass

and a ventral mass. . The dorsal mass will develop into extensor muscles primarily while the

ventral mass will develop into flexor muscles primarily. This pattern can be seen in fishes and

tetrapods. In some amniotes (such as humans) this pattern is harder to see since the limb has

become rotated but it does still exist. These muscles are easily observed after skinning Necturus.

Only judicious application of the separating technique with the tips of your scissors will be

needed to better define the borders of most muscles.

The dorsal muscles of the pectoral girdle tend to be thin muscles that originate from

fascia of neighboring epaxial muscles. It is this loose attachment that makes them easy to

remove or damage during skinning. The latissimus dorsi and cucullaris (which is homologous to

the trapezius) are much smaller, thinner, and more weakly attached than is seen in amniotes. The

cucullaris is of a different embryonic origin than are other muscles being a branchiomeric muscle

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instead of a somatic muscle. The dorsal muscles of the pectoral girdle include the latissimus

dorsi, cucullaris, pectoriscapularis, and the dorsalis scapulae. The dorsalis scapulae is most

likely homologous to the deltoid. The muscles of the ventral pectoral girdle are the pectoralis,

supracoracoideus, and procoracohumeralis. The pectoralis and supracoracoideus have close, but

slightly different insertions, allowing for different ranges in the movements produced by them.

The arm of Necturus has three muscles. One is the triceps brachii, which has three points of

origin (or heads) and serves as an antagonist to the other two muscles. The other two are the

humeroantebrachialis and the coracobrachialis. These muscles are synergists to one another,

producing flexion of the forearm. They can be distinguished from each other by the fact that the

coracobrachialis is the more medial of the two muscles. The humeroantebrachialis, although it

has only one point of origination, is homologous to the biceps brachii.

Procoracohumeralis Cucullaris Humeroantebrachialis

Omoarcual Triceps Brachii External Abdominal Oblique

Pectoriscapularis Dorsalis Scapulae Latissimus Dorsi

Necturus Myology of the Pectoral Girdle and Forelimb, Dorsal View

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Geniohyoid Branchiohyoid Rectus Cervicis Procoracohumeralis Humeroantebrachialis

Omoarcual Coracohumeralis

Intermandibularis Interhyoid Supracoracoideus Pectoralis

Necturus Myology: Branchial Muscles, Forelimb, and Pectoral Girdle

Muscles of the Forelimb and Pectoral Girdle

Muscle Origin Insertion Action

Cucullaris Fascia on dorsalis trunci, cervical portion Scapula Move scapula craniodorsally

Pectoriscapularis Fascia on dorsalis trunci, cervical portion Scapula Move scapula cranially

Dorsalis scapulae Suprascapular cartilage Humerus Abduct humerus

Latissimus dorsi Fascia of dorsalis trunci, thoracic portion Humerus Move humerus caudally

Procoracohumeralis Procoracoid cartilage Humerus Move humerus cranially

Supracoracoideus Linea alba on coracoid Humerus Adduct humerus

Pectoralis Linea alba on coracoid Humerus Adduct humerus

Triceps Brachii Coracoid, Scapula, & Humerus Ulna Extends forearm

Humeroantebrachialis Humerus Radius Flexes forearm

Coracobrachialis Coracoid Humerus Flexes forearm

While the components of the pectoral girdle are loosely attached to one another and are

capable of independent movement, such is not the case with the pelvic girdle. The elements of

the pelvic girdle are tightly joined together and are also joined to the vertebral column

(especially in amniotes). So unlike pectoral girdle muscles which can originate on the axial

83

skeleton and inserting on the girdle, pelvic girdle muscles originate on the pelvis and insert into

the limb. The locomotory muscles of the posterior limb extend from bones/cartilages of the

pelvic girdle (ilium, ischium, and pubis) to the femur and/or the fibula/tibia, from the femur to

the tibia/fibula, and from the tibia/fibula to the bones of the pes. In modern amphibians and

reptiles the muscles are typically named for their origin and insertion. Such is the case with most

of the pelvic and hind limb muscles of Necturus. These muscles tend to have broad insertions.

This causes them to lack the more precise movements that we see in amniotes. For example, the

ischioflexorius inserts over a broad area of the tibia and the plantar fascia of the pes. There are

five pairs of ventrally oriented muscles: puboischiofemoralis externus, puboischiofemoralis

internus, pubotibialis, puboischiotibialis, and ischioflexorius. Due to the shape of the

puboischiadic plate the origin of the puboischiofemoralis externus comes to a notable point.

There are three pairs of dorsally oriented muscles: iliotibialis, ilioextensorius, and iliofibularis.

Puboischiofemoralis Externus Puboischiotibialis

Pubotibialis Puboischiofemoralis Internus

Necturus Muscles of the Pelvic Girdle and Hind Limb, Ventral View

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External Abdominal Oblique Iliotibialis Ilioextensorius Iliofibularis

Necturus Muscles of the Pelvic Girdle and Hind Limb, Dorsal View

Muscles of the Pelvis and Hind Limb

Muscle Origin Insertion Action

Puboischiofemoralis externus Puboischiadic plate Femur Adducts femur

Puboischiofemoralis internus Puboischiadic plate Femur Moves femur anteriorly

Pubotibialis Pubis Tibia Adducts femur & extends leg

Puboischiotibialis Puboischiadic plate Tibia Adducts femur & flexes leg

Ischioflexorius Ischium Tibia & Pes Flexes leg & foot

Iliotibialis Ilium Tibia Extends leg

Ilioextensorius Ilium Tibia Extends leg

Iliofibularis Ilium Fibula Extends leg

Topic C3: The Muscles of Felis

In amniotes such as Felis the appendicular muscles display little of the metameric pattern

that we saw with Squalus and Necturus. The epaxial muscles of amniotes are strap-like and run

the length of the vertebral column, extending from the base of the skull into the tail to varying

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extents. These muscles function to extend the vertebral column and to laterally flex the torso and

are collectively known as the erector spinae muscles. Epaxial muscles are divided into four

groups: intervertebrals, longissimus, spinales, and iliocostales. The intervertebral muscles are the

deepest epaxials and are the only ones to retain the metameric condition. They help to maintain

posture. The multifidus spinae will be the only one visible in this dissection. The longissimus is

the longest epaxial muscle. It is located dorsal and lateral to the transverse processes of the

vertebrae. The longissimus is the dominant extensor of the mammalian vertebral column

although it does not usually play a role in mammalian locomotion. This muscle typically has

three bundles that insert in varying locations. The bundles are named for these points of

insertion: longissimus capitis inserts on the head, longissimus cervicis inserts on the neck, and

longissimus dorsi inserts on the trunk. In the lumbar region the longissimus dorsi has three

distinct bundles with the medial bundle extending into the tail to form the extensor caudae

lateralis. You can observe these three bundles by cutting and reflecting a portion of the multi-

layered lumbodorsal aponeurosis. The spinales are also located dorsal to the transverse processes

and medial to the longissimus. There are a number of spinales muscles including spinalis capitis,

spinalis cervicis, and spinalis dorsi. The iliocostales are a thin sheet of muscles originating on the

ilium and inserting on the ribs. The spinalis dorsi, longissimus dorsi, and iliocostalis can be

observed by cutting and reflecting the spinotrapezius and latissimus dorsi. This will expose a

portion of aponeurosis in the thoracic region that can be carefully removed to show the spinalis

dorsi and longissimus dorsi. A third muscle will be visible ventral to the longissimus dorsi, the

serratus dorsalis. The serratus dorsalis displays a segmental pattern and serves to help stabilize

the vertebral column. It has two portions: serratus dorsalis cranialis and serratus dorsalis

caudalis. They can be differentiated by the fiber pattern. Gently peel the serratus dorsalis from

its attachment to the longissimus to observe the iliocostalis. You should be able to observe

tendons of the iliocostalis attaching to the ribs. The epaxial muscle of the dorsal neck is the

splenius and can be observed by cutting and reflecting the clavotrapezius.

Felis Erector Spinae Muscles

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Felis Erector Spinae MusclesErector Spinae Muscles of Felis

Muscle Origin Insertion Action

Serratus Dorsalis, Cranialis R1-R9 Mid-dorsal Raphe Pulls ribs cranially

Caudalis R10-R13 Lumbar Vertebrae Pulls ribs caudally

Longissimus dorsi Sacral and Caudal Vertebrae Thoracic & Cervical Vertebrae, Occipital Extends vertebral column

Spinalis Dorsi T10-T13 Thoracic & Cervical Vertebrae Extends vertebral column

Iliocostalis Ilium Ribs Laterally flexes spine

Splenius Mid-dorsal fascia line Occipital Raises head dorsally

Multifidus Dorsi Vertebral transverse processes Spinous process of vertebra cranial to origin Extends vertebral column

Hypaxial muscles can be broken up into four groups: subvertebrals, oblique sheets,

transverse sheets, and the rectus abdominis. Subvertebral muscles are longitudinally arranged

muscles located deep to the transverse processes in the roof of the coelom from atlas to pelvis.

They are fairly powerful flexors of the spine and serve as antagonists to the epaxial muscles. Due

to their location they will not be a part of this dissection. Oblique and transverse muscles are

located in the lateral body wall and as a result are sometimes referred to as “parietals”. Felis will

have the same oblique and transverse muscle sheets that we saw in Necturus: external abdominal

oblique, internal abdominal oblique, and transversus abdominis (running superficial to deep).

These are very thin muscles and you must be careful when exposing them. You will be able to

differentiate these three muscles by their fiber patterns. Mammals also have a diaphragm that is

the main muscle for respiration. The diaphragm is an oblique muscle. The cremaster muscle is an

outgrowth of the internal abdominal oblique muscle and is found in male mammals. It is a

portion of the spermatic cord and serves to retract the testes. The rectus muscles are limited to

the anterior abdominal wall. Along with the oblique and transverse muscles, the rectus muscles

form a muscular sling to support the viscera. There are two rectus muscles. One is the rectus

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abdominis which is found in all tetrapods. It extends the length of the abdomen, on either side of

the linea alba, from pubis to sternum and assists in flexing the trunk. The second is the

pyramidalis. It is an outgrowth of the rectus abdominis and is found only in mammals. It serves

to support the pouch in marsupials and is vestigial in placental mammals.

Felis Abdominal Muscles

Felis Abdominal Muscles

Muscle Origin Insertion Action

External Abdominal Oblique Lumbodorsal Aponeurosis & Ribs Linea Alba and Pubis Twists trunk

Internal Abdominal Oblique Lumbodorsal Aponeurosis Linea Alba Twists trunk

Transversus Abdominis R10-R13 Linea Alba Twists trunk

Rectus Abdominis Sternum & Ribs/Pubis Pubis/ Sternum & Ribs Flexes trunk

Branchiomeric muscles are found in all amniotes including Felis. In amniotes the

branchiomeric muscles still operate the jaws but the muscles that were once of the gill arches

now serve other purposes. In all gnathostomes the muscles of the first arch, the mandibular arch,

are chiefly jaw muscles. In tetrapods the adductor mandibulae has expanded and developed into

up into three muscles: masseter, temporalis, and pterygoideus. These three muscles have spread

over the skull and provide the bulk off the force for jaw movements. The intermandibularis of

Squalus and Necturus has become the mylohyoid in tetrapods. A portion of the intermandibularis

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may have also given rise to the anterior belly of the digastric muscle. In tetrapods hyoid arch

muscles continue to serve some of the same functions in tetrapods as they did in fishes but they

will also have some new roles. In urodeles and many reptiles the muscles of the second arch give

rise to the depressor mandibulae which serves to open the mouth. In mammals the depressor

mandibulae becomes the posterior belly of the digastric muscle. In amphibians and lower reptiles

a thin sheet of muscle called the sphincter colli is superficial to the branchiohyoideus. In higher

reptiles the sphincter colli extended upwards on to the skull and became the platysma. The

platysma increased in size in mammals and gave rise to the muscles of facial expression. These

are really modified cutaneous muscles and care must be taken when removing the skin so as to

avoid damaging these muscles. Mammals also have a stylohyoid muscle which serve to attach

the hyoid to the styloid process of the skull. The branchiomeric muscles of arches 3 through 7

have been pretty much lost in tetrapods. The remaining muscles from the third arch are:

stylopharyngealis (for swallowing) and stylohyoid (posterior belly) in some mammals. In

mammals the muscles remaining from the fourth arch are the intrinsic muscles of the mammalian

larynx: cricothyroid, cricoarytenoid, and thyroarytenoid. The trapezius, a branchiomeric muscle

of the amniote pectoral girdles, is actually a derivative of the cucullaris.

Felis Superficial Neck and Branchiomeric Muscles

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Sternothyroid Thyrohyoid Hyoglossus Genioglossus Geniohyoid (Digastric & Mylohyoid cut)

Sternomastoid Clavotrapezius Stylohyoid Mylohyoid Digastric

Sternohyoid Masseter

Felis Tongue and Neck Muscles

In the head and neck of Felis we will also find hypobranchial and tongue muscles.

Hypobranchial and tongue muscles are anterior extensions of the hypaxial muscles. The

hypobranchial muscles of amniotes include: sternomastoid, cleidomastoid, sternohyoid,

sternothyroid, thyrohyoid, and geniohyoid. The sternothyroid and thyrohyoid may be observed

by cutting and reflecting the sternohyoid. The muscles of the tongue develop from mesenchyme

that has migrated from anterior hypobranchial muscle blastemas. Tongue muscles can be either

extrinsic or intrinsic. Extrinsic tongue muscles originate outside of the tongue (on the hyoid or

chin for example) and insert in the tongue. They include the genioglossus, hyoglossus, and

styloglossus. These muscles may be observed but cutting and reflecting the mylohyoid. Intrinsic

tongue muscles originate and insert in the tongue. They are restricted to mammals, birds, and

some retiles. Since hypobranchial and tongue muscles originate from the anteriormost somites

of the trunk they are innervated by cervical spinal nerves in general, although CN XII will play a

role in some cases.

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Felis Tongue and Neck Muscles

Felis Tongue and Neck Muscles

Muscle Origin Insertion Action

Sternomastoid Manubrium Temporal Laterally flex neck

Sternohyoid Manubrium Hyoid Pulls hyoid posteriorly

Digastric Basioccipital Mandible Depresses mandible

Mylohyoid Mandible Median Raphe Raises floor of mouth

Stylohyoid Stylohyal Hyoid Elevates hyoid

Masseter Zygomatic Arch Mandible Elevates mandible

Temporalis Temporal Fossa Mandible Elevates mandible

Sternothyroid Manubrium Thyroid cartilage Pulls larynx caudally

Thyrohyoid Thyroid cartilage Hyoid Raises larynx

Cricothyroid Cricoid cartilage Thyroid cartilage Puts tension of the vocal cords

Cleidomastoid Clavicle Temporal Laterally flex neck

Geniohyoid Mandible Hyoid Pulls mandible cranially

Hyoglossus Hyoid Tongue Retracts tongue

Styloglossus Stylohyal Tongue Retracts tongue

Genioglossus Mandible Tongue Protracts base of tongue

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As has been mentioned previously, the appendicular muscles of tetrapods are more

numerous and complex than are those of fishes. In Felis the appendicular muscles are larger and

more diverse than those of Necturus. One example is the latissimus dorsi. It is a primary

appendicular muscle that inserts on the humerus. It has increased in size, strength, and the size of

its attachments over evolutionary time. In Necturus the latissimus dorsi is a thin triangular

muscle arising from fascia superficial to the epaxial myomeres of the shoulder region. In

mammals the origin covers a much greater area of the dorsal body and is directly on the spinous

processes of the vertebrae (most thoracic, all lumbar, some sacral, and even some caudal

vertebrae). The size of the latissimus dorsi and area of insertion on the humerus has also

increased.

Deep to the latissimus dorsi in Felis are three extrinsic muscle groups that insert on the scapula.

These three groups are the two levators of the scapula, the rhomboideus muscles, and the serratus

ventralis. The levators of the scapula in Felis are the levator scapulae ventralis and the levator

scapulae dorsalis. The rhomboideus group in Felis is composed of three pairs of muscles that

move the scapula and differ in their point of origin. Originating on the occipital bone is the

rhomboideus capitis (a.k.a.; occipitoscapularis). Originating on the cervical vertebrae is the

rhomboideus minors. The broadest origin is that of the rhomboideus major which originates on

some of the cervical and thoracic vertebrae. The serratus ventralis originates from some of the

ribs and inserts on the scapula. It can be seen in the axillary region immediately caudal to the

levator scapulae dorsalis (a.k.a.; levator scapulae) and ventral to the serratus dorsalis. The

trapezius of tetrapods is derived from the cucullaris of fish and is of branchiomeric origin. The

trapezius, like the latissimus dorsi, has increased in size over evolutionary time. In mammals it

has three portions: clavotrapezius, acromiotrapezius, and spinotrapezius. These three muscles

differ in their point of insertion to the pectoral girdle. Due to its evolutionary origin the trapezius

receives innervation from branchiomeric nerves, which is unique in appendicular muscles.

Felis Superficial Back and Dorsal Arm Muscles

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Felis Deep Upper Back Muscles

Felis Upper Back Muscles

Muscle Origin Insertion Action

Clavotrapezius Lambdoidal Crest Clavicle Dorsally raise scapula

Acromiotrapezius Cervical Vertebrae Scapula Dorsally raise scapula

Spinotrapezius Thoracic Vertebrae Scapular muscle fascia Dorsally raise scapula

Clavobrachialis Clavicle Ulna Flexes forearm

Acromiodeltoid Scapula Humerus Flex and rotate humerus

Spinodeltoid Scapula Humerus Flex and rotate humerus

Levator Scapulae Ventralis C1 and Occipital Scapula Raises scapula cranially

Latissimus Dorsi Thoracic & Lumbar Vertebrae Humerus Pulls arms caudodorsally

Rhomboideus Major Cervical &Thoracic Vertebrae Scapula Pulls scapula dorsally

Rhomboideus Minor Cervical Vertebrae Scapula Pulls scapula dorsally

Rhomboideus Capitis Occipital Scapula Pulls scapula cranially

Supraspinatus Scapula Humerus Extends humerus

Infraspinatus Scapula Humerus Laterally rotates humerus

Teres Major Scapula Humerus Medially rotates humerus

Teres Minor Scapula Humerus Laterally rotates humerus

The ventral muscles of the pectoral girdle are collectively referred to as the “pectorals”.

These muscles have undergone expansive changes over evolutionary time due to an increased

need for strength. Primitively it originated on the coracoid cartilages (or bones) and a midventral

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raphe on the neck as we saw in Necturus. In mammals it originates on the bones of the sternum

and some ribs. Over time the pectorals developed from one thin muscle into a varying number of

superficial and deep muscles. In Felis the pectoralis has developed into four muscles pairs. They

are the: pectoralis major, pectoralis minor, xiphihumeralis, and pectoantebrachialis. Deep to the

superficial pectoral muscles are small, strap-like muscles that help to move the ribs. By cutting

and reflecting the pectoral muscles you may observe: transversus costarum, scalenus (anterior,

medius, and posterior), and the external and the internal intercostals.

In Felis there are five postaxial muscles that originate on the scapula and insert on the

humerus. One easily observed muscle is the deltoid. Although the deltoid is a single muscle in

humans, in Felis and most other mammals it is actually three muscles: clavodeltoid (a.k.a.;

clavobrachialis), acromiodeltoid, and spinodeltoid. The deltoid is believed to be homologous to

the dorsalis scapulae that you saw in Necturus. Another muscle is the teres major. The teres

major most likely developed from a slip of the latissimus dorsi. An antagonist to the teres major

is the teres minor, both causing rotation of the humerus. The subscapularis is another of these

muscles and originates from the subscapular fossa. In Felis there are also three ventral muscles

from the scapula that serve to flex the arm. They are the: supraspinatus, infraspinatus, and

coracobrachialis. The supraspinatus and infraspinatus originate from the dorsal scapula (the

supraspinous and infraspinous fossae respectively). This, however, is a modified condition and

these muscles developed from the ventral extrinsic muscle of reptiles called the

supracoracoideus. So they are truly ventral muscles.

Felis Superficial Chest Muscles and Ventral Superficial Arm Muscles

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Rectus Abdominis Scalenus Medius Transversus Costarum Scalenus Anterior Scalenus Posterior

Serratus Ventralis Levator Scapulae Subscapularis Teres Major

Felis Deep Chest Muscles

Felis Chest Muscles

Muscle Origin Insertion Action

Pectoantebrachialis Manubrium Fascia of forearm Adducts forelimb

Pectoralis Major Sternebrae Humerus Adducts forelimb

Pectoralis Minor Sternebrae Humerus Adducts forelimb

Xiphihumeralis Xiphoid process Humerus Adducts forelimb

Serratus Ventralis R1-R10 Scapula Pulls scapula ventrally

Levator Scapula C3-C7 Scapula Raises scapula cranially

Scalenus Ribs Cervical Vertebrae Flexes neck

External Intercostal Border of rib Border of adjacent rib Expands ribcage

Internal Intercostal Border of rib Border of adjacent rib Compresses ribcage

The muscles of the arm will typically extend (dorsal muscles) or flex (ventral muscles)

the forearm. In Felis the triceps brachii is a well developed muscle. It has three heads. The long

head originates from the infraglenoid tubercle of the scapula and inserts on the olecranon. The

two other heads (the lateral and medial heads will originate on the humerus and also insert on the

olecranon. Mammalian ventral muscles that insert and flex the forearm include: biceps brachii,

brachialis, anconeus, and epitrochlearis. The biceps brachii is homologous to the

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humeroantebrachialis that you observed in Necturus. When removing the fascia from these

muscles work from the shoulder towards the elbow. Do not go below the elbow until the fascia is

removed from all of the arm muscles. The tendons of the arm muscles will blend in with a tough

connective tissue sheath superficial to the forearm muscles called the retinaculum. It is difficult

to separate the tendons (which you want to save) from the retinaculum until you can see the arm

muscles clearly.

Felis Superficial Dorsal Arm Muscles

Felis Arm Muscles

Muscle Origin Insertion Action

Triceps Brachii Scapula & Humerus Ulna Extends forearm

Anconeus Humerus Ulna Extends forearm

Epitrochlearis Latissimus dorsi, ventral border Ulna Extends forearm

Brachialis Humerus Ulna Flexes forearm

Biceps Brachii Humerus Radius Flexes forearm

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Felis Deep Dorsal Arm Muscles

Felis Deep Ventral Arm Muscles

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The muscles of the forearm in Felis can seem confusing but are easy to learn if you

remember two things. The dorsal muscles of the forearm are the supinators and extensors of the

wrist, manus, and digits while the ventral muscles of the forearm are the pronators and flexors of

the wrist, manus, and digits. The other thing to remember is which side of the forearm the ulna

is on and which side the radius is on. On the dorsal forearm the superficial muscles running

from radial side to ulnar side are: brachioradialis, extensor carpi radialis longus, extensor carpi

radialis brevis, extensor digitorum communis, extensor digitorum lateralis, and extensor carpi

ulnaris. On the ventral forearm the superficial muscles running from the ulnar side to the radial

side are: flexor carpi ulnaris, palmaris longus, flexor carpi radialis, and pronator teres. One

dorsal, superficial muscle that you must be careful with is the brachioradialis. This is a very thin

muscle in Felis and can easily be removed with the skin. Be very careful when skinning the

forearm to avoid this.

Felis Superficial Dorsal Forearm Muscles

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Felis Superficial Ventral Forearm Muscles

Felis Forearm Muscles

Muscle Origin Insertion Action

Brachioradialis Humerus Radius Supinates forepaw

Extensor Carpi Radialis Longus Humerus Carpals Extends wrist/paw

Extensor Carpi Radialis Brevis Humerus Carpals Extends wrist/paw

Extensor Digitorum Communis Humerus Metacarpals Extends digits

Extensor Digitorum Lateralis Humerus Lateral Metacarpals Extends lateral digits

Extensor Carpi Ulnaris Humerus Carpals Extends wrist/paw

Flexor Carpi Ulnaris Humerus & Ulna Carpals Flexes wrist

Palmaris Longus Humerus Palmar Fascia Flexes palm & digits

Flexor Carpi Radialis Humerus Carpals Flexes wrist

Pronator Teres Humerus Radius Pronates forepaw

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Felis Superficial Buttocks and Lateral Thigh Muscles

Felis Buttocks and Thigh Muscles

Muscle Origin Insertion Action

Gluteus Medius Sacral & Caudal Vertebrae Femur Abducts thigh

Gluteus Maximus Sacral & Caudal Vertebrae Femur Abducts thigh

Caudofemoralis Caudal Vertebrae Patella Abducts thigh & Extends leg

Tensor Fascia Latae Ilium IT Band Tighten IT band

Tenuissimus 2nd Caudal Vertebra Patella Abducts thigh

Biceps Femoris Ischium Patella & Tibia Flexes leg

Semitendinosus Ischium Tibia Flexes leg

Sartorius Ilium Tibia Adducts & Rotates thigh

Gracilis Ischium & Pubic Symphysis Tibia Adducts thigh

Semimembranosus Ischium Femur Extends thigh

Adductor Magnus Ischium & Pubis Femur Adducts thigh

Adductor Longus Pubis Femur Adducts thigh

Pectineus Pubis Femur Adducts & Extends thigh

Iliopsoas Ilium & Lumbar Vertebrae Femur Rotates and Flexes thigh

Rectus Femoris Ilium Patella Extends leg

Vastus Medialis Femur Patella Extends leg

Vastus Lateralis Femur Patella Extends leg

Vastus Intermedius Femur Patella Extends leg

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Felis Superficial Ventral Thigh Muscles

The muscles of the buttocks will have their origins partially covered by the lumbodorsal

aponeurosis. As a result, care must be taken when removing the fascia from them. When the

origins begin to fray you have removed as much fascia from that area as is reasonably possible.

The superficial buttocks muscles will be the caudofemoralis, gluteus medius, and gluteus

maximus. The gluteus medius is actually the larger gluteal muscle while the gluteus maximus is

a thin flap of muscle in Felis. The tendon of the caudofemoralis will run beneath the biceps

femoris to insert on the patella. Immediately lateral to the gluteal muscles is the tensor fascia

latae. This muscle is attached to a broad tendon called the lateral fascia or iliotibial tract or IT

band. Take care not to damage this tendon until it is time to go deep. The superficial lateral

thigh muscles are the semitendinosus and biceps femoris. The biceps femoris is a large muscle

having prominent fascicles and will be close to the integument. Cutting and reflecting the biceps

femoris will make it easier to see the semitendinosus and a ventral thigh muscle, the

semimembranosus. While reflecting the biceps femoris, you can observe two slender structures

beneath the muscle, the sciatic nerve and the tenuissimus muscle. The tenuissimus is a slender

muscle that resembles a fascicle that broke free from the biceps femoris and will be smaller than

the sciatic nerve. The ventral superficial thigh muscles are the sartorius, gracilis, and

semimembranosus. In Felis the sartorius is a broad, flap-like muscle covering much of the

medial thigh and is visible on the lateral surface of the thigh as well. This is different from the

sartorius in humans which is a thin, strap-like muscle running from the ilium, across the thigh, to

the medial epicondyle. By cutting and reflecting the sartorius and the iliotibial tract you can

observe the quadriceps. Three of the four muscles are immediately apparent. These are the

vastus lateralis (beneath the iliotibial tract), rectus femoris, and vastus medialis (both are below

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the sartorius). Cutting and reflecting the cigar-shaped rectus femoris will allow you to observe

the fourth muscle, the vastus intermedius. You will also cut and reflect the gracilis in your deep

dissection. This will expose the adductor muscles and make it easier to observe the

semimembranosus and semitendinosus. In Felis there are three adductor muscles; the adductor

magnus (a.k.a.; adductor femoris), adductor longus, and pectineus. After removing some fat and

fascia from the ventral junction of the hip and thigh you will be able to observe a small muscle

anterior to the pectineus. This muscle is the iliopsoas and it runs roughly perpendicular to the

neighboring inner thigh muscles. The iliopsoas is actually two muscle, iliacus and psoas major

that have fused together. When removing fascia from the thigh muscles care must be taken to

preserve their tendons of insertion, as was the case with the arm muscles. Again work from the

girdle out. Do not work below the knee until the thigh muscles are fully exposed to avoid

damaging these tendons.

A prominent feature of the leg is the calf muscle. The "calf" is actually two muscles that

share the calcaneal tendon. The superficial muscle is the gastrocnemius. Immediately deep to it is

the soleus. The soleus can also be distinguished from the gastrocnemius by its bipennate fiber

pattern. The soleus is more easily observed on the medial aspect of the leg. On the lateral aspect

you will see the flexor hallucis longus. The soleus is actually sandwiched between the

gastrocnemius and flexor hallucis longus on the lateral aspect but the soleus is hard to see on this

side. On the posterior-medial aspect of the leg you can observe the tibialis posterior and flexor

digitorum longus running between the soleus and tibia. Anterior to the tibia will be two muscles,

the tibialis anterior and the extensor digitorum longus. On the lateral aspect of the leg are three

slender muscles called the peroneals (a.k.a.; fibulares). The larger, more anterior peroneal

muscle is the peroneus longus. Posterior to it is the smaller peroneus tertius. Both muscles look

similar having the muscle below the knee and tapering into a slender tendon. Between the two is

the third peroneal muscle, the peroneus brevis.

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Vastus Lateralis Vastus Medialis Rectus Femoris

Vastus Intermedius Rectus Femoris (half reflected)

Felis Quadriceps, Two Views

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Felis Lateral Shin Muscles

Felis Leg Muscles

Muscle Origin Insertion Action

Gastrocnemius Femur Calcaneus Extends hindpaw

Soleus Tibia Calcaneus Extends hindpaw

Flexor Digitorum Longus Fibula & Tibia Phalanges Flexes digits

Flexor Hallucis Longus Fibula & Tibia Phalanges Flexes digits

Tibialis Posterior Fibula & Tibia Lateral Cuneiform Extends hindpaw

Tibialis Anterior Fibula & Tibia First Metatarsal Flexes hindpaw

Extensor Digitorum Longus Femur Phalanges Extends hindpaw

Peroneus Longus Fibula Metatarsals Flexes hindpaw

Peroneus Brevis Fibula 5th Metatarsal Extends hindpaw

Peroneus Tertius Fibula Metatarsals Extends & Abducts digits

Gastrocnemius Soleus Flexor Hallucis Longus Tibialis Posterior Peroneus Brevis

Tibialis Anterior Extensor Digitorum Longus

Peroneus Peroneus

Longus Tertius

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Felis Anterior Leg Muscles

Felis Medial Leg Muscles

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Part 3: Visceral Organs and Angiology

Part A: Exposing the Visceral Organs and Angiology

Part A1: Exposing the Visceral Organs and Blood Vessels in Squalus

Angiology is the study of blood vessels. Blood vessels are true organs, being composed

of tissues working together to perform a function. The wall of the typical blood vessel is

composed of three “tunics”: the tunica intima, the tunica media, and the tunica adventitia. The

nature of these tunics varies with the class and type of blood vessel. In your dissection you will

be able to observe two of the three classes of blood vessels, arteries and veins. Colored latex has

been injected into the arteries and veins to make them easier to work with and to study. Pink

latex signifies oxygenated blood while blue latex designates deoxygenated blood flow.

Typically oxygenated blood flows through arteries and deoxygenated blood flows through veins.

However, the situation is reversed in the mammalian pulmonary circuit.

To observe the visceral organs and blood vessels it is necessary to open the

pleuroperitoneal cavity. The coelom in most vertebrates is divided into a pericardial cavity and a

pleuroperitoneal cavity. This will be the case in both Squalus and Necturus. The pericardial

cavity contains the heart and the pleuroperitoneal cavity contains the other visceral organs. In

mammals such as Felis the coelom is divided differently. The diaphragm divides the thoracic

cavity from the abdominopelvic cavity. The thoracic cavity can be divided into the pericardial

cavity, two pleural cavities (that contain the lungs), and the mediastinum. The abdominopelvic

cavity can be divided into the abdominal and pelvic cavities. This division does not have a clear

boundary such as the diaphragm. Typically it is demarcated by the rim of the pelvis.

Your Squalus will already have a ventral incision made when the animal’s visceral blood

vessels were injected with latex. You may use this incision as a starting point. Using your fine

point scissors follow the incision as close to midventral as possible. Extend it cranially to the

coracoid bar and caudally to the cloaca. While extending the incision keep your scissors as far

from the pleuroperitoneal cavity as possible so as to avoid damaging the contents. Your next

step is to make two transverse incisions, one below the coracoid bar and one at the ischiopubic

bar. While folding back the hypaxial musculature you will observe that the inner aspect is

“shiny”. This is due to the parietal peritoneum, a serous membrane. You will also observe that

the visceral organs will also be shiny. This is due to the visceral peritoneum. Both the parietal

and visceral peritoneum are one continuous serous membrane. You will also notice folds of the

peritoneum running between the visceral organs and running within these folds will be visceral

blood vessels. To expose these vessels simply use your scissors and the separating technique to

break the vessels free of these peritoneal folds. The blood vessels in Squalus are very fragile and

care must be taken not to damage the vessel wall. In most cases exposing the blood vessel will be

good enough.

To observe the heart you will need to open the pericardial cavity. Take your fine point

scissors and insert them shallowly between the right and left common coracoarcurals. Separate

these two muscles and you will see a white membrane immediately deep to them. This is the

parietal pericardium. The parietal pericardium has a fibrous outer layer and an inner layer that is

a serous membrane. Carefully open the parietal pericardium to observe the heart.

One other area that will need to be opened for your study of vasculature will be the

oropharynx. Using the bone clippers cut through the mandibular arch, the hyoid arch, and the

gill arches at about the point where the ceratobranchial and epibranchial cartilages meet on one

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side. Then using your scissors cut across the ventral oropharynx at the coracoid bar being

careful not to damage the heart. This will expose the roof of the oropharynx. You should be able

to see some of the blood vessels beneath the oral mucosa. To expose these blood vessels peel

back the oral mucosa.

Part A2: Exposing the Visceral Organs and Blood Vessels in Necturus

The technique required to expose the visceral organs and blood vessels in Necturus is

similar to that used for Squalus. To open the pleuroperitoneal cavity you should follow the

incision that was already made to inject the visceral vasculature. Extend this incision to the

pectoral and pelvic girdles. Then make two transverse incisions, one below the pectoral girdle

and one above the pelvic girdle. As with Squalus, be careful to pull up on the scissors so as to

avoid damaging the organs. You will be able to observe the parietal and visceral peritoneum as

you open your specimen. You will be able to observe most of the blood vessels by gently

separating them from the peritoneal folds that they are encased in. Unlike Squalus however, you

will need to follow the vessels on to the limbs. This can be done by following the vessels to their

exit point through the body wall and then separating the muscles concealing them.

To observe the heart you will need to open the pericardial cavity. Take your fine point

scissors and insert them shallowly between the right and left portions of the rectus cervicis along

the median raphe. Separate these two muscle portions and you will see a white membrane

immediately deep to them. This is the parietal pericardium. The parietal pericardium has a

fibrous outer layer and an inner layer that is a serous membrane. Carefully open the parietal

pericardium to observe the heart.

One other area that will need to be opened for your study of vasculature will be the

oropharynx. Using your fine point scissors cut through the jaw joint and the lateral wall of the

oropharynx. Then using your scissors cut across the ventral oropharynx at the coracoid plates

being careful not to damage the heart. This will expose the roof of the oropharynx. You should

be able to see some of the blood vessels beneath the oral mucosa. To expose these blood vessels

peel back the oral mucosa.

Part A3: Exposing the Visceral Organs and Blood Vessels in Felis

The coelom of Felis will need to be approached differently than it was in either Necturus

or Squalus. The abdominopelvic cavity can be opened by using your fine point scissors to make

a midventral incision through the linea alba from the diaphragm to the pubis. Keep the scissors

pulled up to avoid damaging the internal organs. Make a pair of transverse incisions, one

immediately below the diaphragm/last ribs and one at the iliac crest. You will be able to observe

the parietal and visceral peritoneum. You should be able to see how the visceral peritoneum is

reflected from the surface of the urinary bladder onto the rectus abdominis to form the parietal

peritoneum. Unlike Squalus and Necturus, Felis will require more work than simply separating

the vasculature from the peritoneal folds to expose blood vessels. There will also be adipose

tissue. Using the tips of your fine point scissors you will be able to break the fat away using the

separating technique. This step can be tedious and a little frustrating. However, after a while

you should be able to see some results. Often the best approach is to open your scissors parallel

to the blood vessels that you are cleaning. Keep in mind that these vessels should be a milky

pink, milky yellow (hepatic portal system), or a milky blue in color. If you have cleaned the

vessel so that its color is a bright pink, yellow, or blue you have actually removed the blood

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vessel wall and have exposed the latex. This latex will dry out and break on you. You should try

to leave the vessel walls intact.

To open the thoracic cavity you will need to first remove the pectoral musculature. The

rib cage of Felis narrows cranially and it is easy to mistakenly cut through the axillary blood

vessels and brachial plexus. To avoid this use your pressing technique to slice the pectoral

muscles away from their origins along the sternum. You should be able to observe an aperture

where the blood vessels and nerves are exiting the thorax. Place the tip of your bone clipper into

that aperture. Clip through the ribs to about R10. While clipping through the ribs place the

fingers of your non-cutting hand into the thoracic cavity and push on the lungs. This will reduce

the chances that you will accidentally damage these delicate organs. At R10, take your scissors

and cut through the intercostals muscles, along the curve of the ribs, to the sternum. Use your

bone clippers to cut through the sternum and then take your scissors and follow the curve of the

ribs, through the intercostals muscles to the point opposite of where you were clipping through

the ribs. Take the bone clippers and clip through the ribs to the aperture on the opposite side of

where you had started. Now the rib cage can be opened and closed much like the hood of a car.

The anchoring point is the sternohyoid and sternothyroid muscles. Use the pressing technique to

carefully press these muscles away from the neck. This will begin to expose the organs and

blood vessels of the neck.

As was the case with Necturus, you will need to follow the blood vessels into the limbs.

This can be done by following the vessels to their exit point through the body wall and then

separating the muscles concealing them.

Part 3: Visceral Organs and Angiology

Part B: The Respiratory System

The respiratory system will differ markedly between your three anatomical specimens.

All of the organs to be studied in this lab will be part of the conducting portion of the respiratory

system. These are the organs and structures that are involved in ventilation, the exchange of

gases between the water/atmosphere and the gills/lungs. These gases will be exchanged across

the respiratory membrane in external respiration, the exchange of gases between the gills/lungs

and the blood stream. The respiratory membrane will be part of the respiratory portion of the

respiratory system. It will be well vascularized and have a great deal of surface area to increase

the efficiency of this exchange of gases.

Part B1: The Respiratory System in Squalus

Squalus, as is the case with most elasmobranchs, is pentanchid, having 5 pairs of gills.

Along with the gills elasmobranchs also have spiracles. The spiracles can be observed on the

dorsal aspect of the head, posterior to the eyes. Spiracles are modified gills that serve as one-way

intake valves. They are used in rays and skates resting on the sediment to bring in water. The

spiracle evolved into the mammalian eustachian tube. The eustachian tube connects the middle

ear and the pharynx and serves to equalize air pressure in the head.

The gill slits of elasmobranchs are said to be “naked” since, unlike most fishes, they are

not covered by an operculum. Each gill slit opens into a gill chamber. In the first four chambers

the anterior and posterior walls have a demibranch, a well-vascularized gill surface. The fifth

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chamber has a demibranch only on the anterior wall (i.e.; the demibranch is missing from the

posterior wall). The demibranch on the anterior wall is called the pretrematic demibranch. The

demibranch on the posterior wall is called the posttrematic demibranch. Between the

posttrematic demibranch of one gill slit and the pretrematic demibranch of the next gill slit is a

partition called the interbranchial septum. The interbranchial septum is supported by long,

tapering, and sometimes branching cartilaginous gill rays that radiate from the gill cartilages.

Each demibranch’s functional surface consists of large numbers of lamellae of gill mucosa. This

gill mucosa will be well vascularized to maximize the exchange of gasses between gill capillaries

Posttrematic Demibranch Pretrematic Demibranch Gill Slit

Holobranch Interbranchial Septum Demibranch Spiracle

Squalus Dorsal Oropharynx Displaying Gill Structure

and the water. The folds increase surface area for external respiration. A holobranch is composed

of the two demibranchs of a single gill arch (the posttrematic demibranch of the previous gill

chamber and the pretrematic demibranch of the next gill chamber), the associated interbranchial

septum, cartilages, vasculature, nerves, branchiomeric muscles, and associated connective

tissues. The typical pentanchid shark has four holobranchs. Anterior to the first holobranch is the

pretrematic demibranch of the first gill chamber called the first demibranch. Since the fifth

chamber lacks a posttrematic demibranch there is no second demibranch. Elasmobranch gill

arches also have gill rakers. Gill rakers are stubby, projecting structures radiating from the

pharyngeal border to protect the gills from mechanical trauma. Respiratory water enters by the

mouth and spiracles. It exits by way of the gills. Most sharks use ram ventilation but some

species (and the all species of rays and skates) are able to pump water into the pharyngeal

chambers.

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Part B2: The Respiratory System in Necturus

Necturus possesses both gills and lungs. These urodeles are neotenic, showing juvenile

characteristics in the adult. The gills are typically a juvenile condition that will be replaced by

lungs in the mature urodele. Although Necturus develops lungs the gills are retained and fully

functional in the adult animal. The lungs are not used for respiration but instead serve as

hydrostatic organs. The pulmonary artery and vein will be seen prominently on the outer surface

of the lung. The lungs of Necturus are elongated, simple sacs.

The gills are the primary source of respiration. The gills are external and easily observed.

They are feathery, well vascularized structures that can be moved to increase the mount of

oxygen crossing the respiratory surface. The exchange os gases between the water and the

respiratory membrane of the gills will be supplemented by respiration across the integument and

the pharyngoesophageal mucosa.

External Gills Lung

Necturus Gills and Lungs

After opening the oropharynx, observe the roof of the oropharynx. You will be able to

observe the internal nares which penetrate the primary palate. This development first appeared in

rhidipstian fishes and was a modification that allows the nares to be used for ventilation.

Necturus - Internal Nares Penetrating the Primary Palate

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Part B3: The Respiratory System in Felis

In Felis the respiratory system begins with the external nares and nasal cavity. The nasal

cavity is connected to the pharynx by the internal nares. The pharynx begins at the internal nares

and extends down the neck to the level of the glottis. The pharynx communicates with the nose,

mouth, trachea, and esophagus so it serves as a common passageway for air and food. Its walls

are composed of skeletal muscle lined with a mucus membrane. The nature of the mucus

membrane varies regionally. There are three divisions to the pharynx: nasopharynx, oropharynx,

and laryngeopharynx. The nasopharynx is the superior most portion of the pharynx. It lays

posterior to the nasal cavity and extends to the level of the soft palate. It has four openings in its

walls: the two internal nares and the two eustachian tubes. The nasopharynx will exchange air

with the eustachian tubes to stabilize air pressure within the head. The oropharynx is the middle

portion of the pharynx. It extends from the soft palate to the level of the hyoid bone. The

oropharynx has only one opening, the fauces, from the mouth. The laryngeopharynx is a short,

inferior most segment running from the level of the hyoid to the larynx and esophagus.

The larynx is a short passageway between the glottis and trachea. Its walls are supported

by cartilage to withstand air pressure. Most nonmammalian tetrapods have only two pairs of

laryngeal cartilages; the cricoids and arytenoids. Mammals, however, have a greater variety to

the structure of the larynx since they use the greatest range of vocalizations. Most mammals have

the arytenoids and cricoid cartilages and also a third pair, the thyroids. The thyroid and cricoid

cartilages are easily observed and were exposed during your dissection of the neck muscles.

Felis Respiratory Organs Image 1

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The trachea is a singular tube that carries air from the larynx to the lungs. Due to the

vacuum pressure of air during inhalation, cartilaginous plates reinforce the trachea. These plates

are C-shaped, being open dorsally/posteriorly so as to prevent the inhibition of swallowing. The

posterior wall of the trachea instead is composed of a smooth muscle, the trachealis muscle. You

should cut a window into the trachea to observe its internal structure. This is done by making a

three-sided cut. This will cause the cut section to remain attached at one side. In most tetrapods

the trachea ends when it branches into the right and left primary bronchi which will enter into the

right and left lung respectively. This branching point is called the “carina”. The bronchi are

branching structures that serve to conduct air into the various subsegments of the lungs. The

bronchi are structurally similar to the trachea. In mammals the bronchi branch into primary,

secondary, and tertiary bronchi. The tertiary bronchi branch into even smaller branches called

bronchioles. By using the separating technique you should be able to observe the primary and

secondary bronchi.

To observe the trachea and lungs you will need to remove the thymus. The thymus is a

glandular organ of the immune system. It can easily be teased away from the trachea and large

thoracic blood vessels. Interestingly the thymus can be used to determine the age of your animal.

When a mammal reaches puberty the thymus is at its greatest in terms of size and functionality.

The thymus will then begin to degenerate, a process called age-related involution. The

functional tissue will be progressively replaced by adipose tissue. Observe the thymus in your

anatomical specimen before removing it. How much of the thymus is healthy, lobulated tissue

and how much is fat?

Felis Respiratory Organs Image 2

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The lungs are paired, sac like structures that serve as the site of external respiration.

Internally the lungs have a respiratory membrane that will be thin and well vascularized to

increase the efficiency of external respiration. Mammalian lungs are paired structures located in

the thoracic cavity. A muscular diaphragm separates the thoracic and abdominopelvic cavities.

The diaphragm is the primary muscle driving mammalian inspiration. The phrenic nerve controls

the diaphragm. You should be able to observe this nerve running along the inferior vena cava. It

is a branch of the brachial plexus. The diaphragm will be assisted to some degree by the

intercostals. Within the thoracic cavity each lung resides in its own chamber called the pleural

cavity. The two pleural cavities are separated by the mediastinum and pericardial cavity. The

mammalian lungs are highly compartmentalized being broken up into asymmetrical lobes,

lobules, segments, and bronchioles. Each subunit receives its own branches of the respiratory

tree; either bronchi or bronchioles. The smallest bronchioles terminate in alveoli; sac like

structures that serve as the site of external respiration in mammals. Felis has seven lobes to the

lungs, three on the left lung and four on the right lung. The left lung lobes are the: left anterior

lobe, left middle lobe, and left posterior lobe. The right lung lobes are the: right anterior lobe,

right middle lobe, right posterior lobe and (right) mediastinal lobe.

Part 3: Visceral Organs and Angiology

Part C: The Digestive System

The digestive system serves to process food brought into the body (ingestion) through

mechanical and chemical forces. Nutrients are released from the food and absorbed into the

body while indigestible food substances are eliminated from the body. The organs of the

digestive system can be divided into two groups: the gastrointestinal tract/ tube and the accessory

organs.

The gastrointestinal tract is also known a, the G. I. tube, the digestive tube, and as the

alimentary canal. Its nature varies throughout the vertebrates but will typically include the

mouth, esophagus, stomach, small intestine, and large intestine. The mouth, or oropharynx, is

not considered to be a portion of the digestive tube proper. It lacks the basic histology found in

the other organs of the digestive tube. So, although the oral cavity is the entrance into the

digestive tube, it is not structurally similar to the other organs of the digestive tube. The other

organs of the digestive tube have the same four tissue layers or tunics. The tunics will vary to

some degree between the different organs but overall will be fairly consistent. These tunics are:

tunica mucosa, tunica submucosa, tunica muscularis, and tunica serosa. The organs of the

digestive tube proper are very closely related to one another developmentally and evolutionarily

and this is reflected in the similarity of their construction and histology.

The accessory digestive organs are located outside of the digestive tube proper. They

include the: teeth, tongue, extrinsic salivary glands, pancreas, liver, and gall bladder. The

relationship between the accessory digestive organs and the digestive tube is easiest to see with

the accessory glands. Accessory glands, such as the pancreas, exist outside of the tube and

release their products into the digestive tube by way of ducts.

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Part C1: The Digestive System in Squalus

In Squalus the mouth and oropharynx will contain a primary tongue and will be bordered

by numerous teeth arranged into multiple rows. Teeth are lost and replaced through out the

animal’s life, a characteristic termed polyphyodontic dentition. You will notice that the teeth are

all of the same basic shape. This is termed homodontic dentition and is typically a feature of

ectotherms. The primary tongue lacks muscle and so is incapable of independent movement.

It is a crescent-shaped elevation on the floor of the oropharynx that is shaped by the underlying

basihyal and ceratohyal cartilages.

The esophagus is a collapsible, muscular tube extending from the oropharynx to the

stomach. Its primary purpose in vertebrates is to conduct food to the stomach. At the point

where the esophagus meets the stomach there is a circular band of smooth muscle called the

gastroesophageal sphincter (a.k.a.; the cardiac or lower esophageal sphincter). The esophagus of

Squalus will have short, stubby evaginations of the tunica mucosa called esophageal papillae. It

is speculated that these evaginations may help to keep prey trapped in the digestive tract.

The stomach is a muscular outpocketing of the digestive tract that serves to store food.

The stomach can store food for an amazing length of time in sharks. There are documented

cases of captive sharks storing food in the stomach for up to a year. To allow for the storage of

food the stomach must be able to distend. The tunica mucosa will be arranged into folds called

rugae that allow the stomach to stretch. Rugae are found in all vertebrates that possess a

stomach. You should cut a window into the stomach. The stomach contents may be interesting

and an empty stomach will display the rugae. The stomach will have two sphincters associated

with it; the cardiac sphincter and the pyloric sphincter (located between the stomach and small

intestine). In Squalus the stomach is a J-shaped organ having a greater and a lesser curvature.

There are three portions to the elasmobranch stomach. The first portion is the cardia. It is

located where the esophagus meets the stomach. The short, middle portion is called the body.

The stomach will have a narrowing portion where the stomach meets the small intestine called

the pylorus. Peritoneal folds will extend off of the gastric tunica serosa. One extends between

the stomach and liver and is termed the lesser omentum. Another attaches the stomach to the

dorsal pleuroperitoneal wall and is called the mesogaster.

In Squalus, as is the case with most fishes from agnathans through teleosts, the intestine

is typically a straight tube from the stomach to cloaca. In chondrichthyes and certain other

nonteleost fishes the intestine has a spiral valve (a.k.a.; typhosole) that serves to increase surface

area to enhance the efficiency of digestion and nutrient absorption. This portion of the intestine is

called the spiral intestine. Some anatomists choose to consider the spiral intestine, and the short

segment before it, to be portions of the small intestine. The spiral intestine would be the ileum

and the short segment between it and the stomach would be the duodenum. You should a cut a

window into the ileum to observe the spiral valve. A peritoneal fold, called the mesentery

extends from the intestinal tunica serosa to anchor the organ to the dorsal pleuroperitoneal wall.

The portion of the intestine after the spiral valve is called the postvalvular intestine. Those

anatomists who subdivide the chondrichthyan intestine consider the postvalvular intestine to be

the colon of the large intestine. This segment will empty into the cloaca. In chondrichthyes

connected to the postvalvular segment of the intestine is the rectal gland. The rectal gland serves

for osmoregulation and does not play a role in digestion. A peritoneal fold arises from the tunica

serosa of both the rectal gland and the colon called the mesorectum. It serves to attach both

organs to the dorsal pleuroperitoneal wall.

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Esophagus Stomach: Cardia Pylorus Body Ventral Lobe of Pancreas Spleen

Small Intestine: Duodenum Ileum/Spiral Intestine Spiral Valves

Squalus Digestive Organs 1

Colon Cloaca

Rectal Gland

Squalus Colon and Rectal Gland

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The accessory digestive organs of Squalus include the liver, gall bladder, and pancreas.

The liver is a prominent gland found in the cranial two thirds of the pleuroperitoneal cavity. It

will have a great deal of oil inside of it. This oil allows the shark to use the liver as a hydrostatic

organ. The liver will produce bile for the break down of lipids. This accessory organ is well

vascularized. It receives nutrient rich blood from the stomach and intestine for processing. The

series of blood vessels that connect the liver to the stomach and intestine make up the hepatic

portal system. The liver of Squalus has a right, left, and median lobe. A peritoneal fold, the

falciform ligament, attaches the liver to the midventral body wall. Along the caudal apex of the

median lobe is the gall bladder. The gall bladder stores bile produced by the liver. The gall

bladder releases bile into the intestine near the pyloric junction by the cystic duct. An organ

located along the greater curvature of the stomach that may be mistaken for a lobe of the liver is

the spleen. Like the liver, the spleen is a well-vascularized organ. It serves as a portion of the

immune system and also serves as a reservoir for blood. The pancreas is a glandular organ that

produces a wide variety of digestive enzymes and buffering agents. In Squalus it has two

separate lobes. The ventral lobe is located on the ventral aspect of the duodenum near the

pyloric junction. The dorsal lobe is an elongated structure located dorsal to the stomach.

Running through the dorsal lobe of the pancreas is the lienomesenteric vein.

Pancreas: Ventral Lobe

Squalus Digestive Organs 2

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Part C2: The Digestive System in Necturus

The digestive system of Necturus is similar to that of Squalus. The mouth and

oropharynx will contain a primary tongue and have a homodontic dentition, although the number

of tooth rows is much reduced. The oropharynx opens into an esophagus. This muscular tube

will conduct food from the oropharynx into the stomach. It is separated from the stomach by the

cardiac sphincter.

The stomach in Necturus is a J-shaped structure and will show a greater and a lesser

curvature. There are three portions to the stomach in Necturus: the cardia, the body, and the

pylorus. It is difficult to distinguish the cardiac region from the esophagus in Necturus. One

landmark is the attachment point of the gastric artery. That will be at the cardia. A peritoneal

fold from the gastric tunica serosa, the gastrosplenic ligament, will attach the spleen to the

stomach at the cardia. Ventrally another peritoneal fold called the hepatogastric ligament

attaches the liver to the stomach. A third peritoneal fold will attach the stomach to the dorsal

pleuroperitoneal wall called the mesogaster. The tunica mucosa will be arranged into rugae when

the stomach is empty. You should cut a window into the body of the stomach. Many times the

stomachs of these animals will contain crayfish and/or minnows. The stomach and small

intestine meet at the pyloric junction which will contain the pyloric sphincter.

The intestines of Necturus can be divided into the small and large intestines. Unlike

Squalus, the intestines of Necturus are not straight. They will show a slight degree of coiling.

This is particularly true for the small intestine. The small intestine in Necturus is divided into the

duodenum and ileum. The duodenum is the longer segment and will be responsible for the bulk

of nutrient break down and much of nutrient absorption. The ileum will complete the absorption

of nutrients. The small intestine is attached to the dorsal pleuroperitoneal wall by an

outpocketing of its tunica serosa called the mesentery. The mesentery also runs between the

coils of the small intestine and binds them together. The ileum terminates at the large intestine.

Necturus Digestive Organs 1

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The large intestine of Necturus is composed almost exclusively of the rectum. The

rectum allows for primarily for the storage of feces prior to elimination. It will be attached to the

dorsal pleuroperitoneal wall by an outpocketing of its tunica serosa called the

mesorectum/mesocolon. The rectum will open into the cloaca.

Ileum Duodenum Stomach: Pylorus Body Cardia Liver (retracted) Esophagus

Oviduct Ovary Pancreas Spleen Lung

Necturus Digestive Organs 2

The accessory digestive organs of Necturus include the liver, gall bladder, and pancreas.

The liver is a prominent, grey, glandular organ dominating the ventral aspect of the

pleuroperitoneal cavity. It is lobulated but does not show lobes. As a result, it will appear as one

solid structure. The liver will produce bile. It is attached to the ventral abdominal wall by the

falciform ligament. The gall bladder can be found at the caudal extent of the liver, more on the

right side than midventral. It will store bile produced by the liver to be released into the

duodenum during digestion. The pancreas may be a little hard to distinguish initially. It is

roughly the same color as the duodenum and runs partially along it. You will notice it at the

pyloric junction and should be able to observe the pancreaticoduodenal artery entering it. The

pancreas it an active digestive gland. It will produce a variety of enzymes and buffering agents.

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Part C3: The Digestive System in Felis

The digestive system of amniotes is more complex than is that of fishes or amphibians.

This is especially true for mammals, such as Felis, due to their endothermic nature. Food must be

processed much more rapidly, and efficiently, in endotherms than in ectotherms so as to be able

to maintain a constant internal temperature. Some of these modifications can be observed in and

around the oral cavity. One obvious feature is the cheeks. The cheeks allow and animal to keep

food in its mouth when chewing. You should be able to observe some of the salivary glands that,

unlike nonmammals, will produce enzymes to aid in digestion. You should be able to see the

parotid salivary gland on the posterior aspect of the masseter. The submandibular salivary

glands are found beneath the angle of the mandible. The tongue of Felis has both a primary and

secondary tongue component. The secondary tongue is glandular in nature and mobile. It will

also have keratinized papillae on the dorsal surface to rasp meat off of bone and to groom the fur.

Felis has a heterodontic dentition meaning that the teeth are of variable shapes. This allows for a

division of labor and is found in animals that chew their food. There are four types of teeth in

mammals. Incisors are chisel-shaped teeth designed to bite food. Canines are the fang teeth

designed for tearing meat. Premolars are intermediate shaped teeth that serve to both tear and

crush food. In Felis the premolar is called the carnassials and is modified to shear through

tendons. Molars are the posterior most teeth and serve to crush food. The nature and relative

numbers of these teeth types will vary based on a species mode of feeding. Another feature that

was not observed in either Squalus or Necturus is the presence of a secondary palate. This

divides the nasal cavity from the oral cavity.

Felis Upper Digestive Tract

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Food (or to be more accurate, the bolus) will pass from the oral cavity into the pharynx

and then to the esophagus. The esophagus is a collapsible muscular tube that will transport the

food to the stomach. Unlike the other organs of the digestive tract it lacks a tunica serosa along

much of its length. Instead, the entire esophagus cranial to the diaphragm is covered by the

tunica adventitia. The tunica adventitia is a fibrous connective tissue that anchors the esophagus

to the tunica adventitia of the trachea, the tunica externa of the common carotid arteries, and the

epineurium of the vagus nerves. You will need to use the separating technique to extricate these

structures from each other. Also, due to its muscular nature and outer layer of connective tissue

the esophagus may initially mistaken for a neck muscle. You may wish to cut a window into the

esophagus. Notice how its inner aspect is folded to allow for distension during swallowing. It

will terminate immediately below the diaphragm at the cardiac sphincter at the stomach.

Felis Digestive Organs 1

The stomach of Felis is much like that of humans and is fairly simple for a mammal

(some rodents and ungulates have very complex stomachs). It is a J-shaped organ having a

greater and lesser curvature. Coming off of the greater curvature is a four-layered fold of the

tunica serosa called the greater omentum. The greater omentum hangs over the intestines. It will

contain ribbons of fat. Due to its location and appearance it is sometimes referred to as the “fatty

apron”. After opening the abdominopelvic cavity you will need to carefully remove this

peritoneal structure. Take care when removing it from the pancreas and spleen to avoid loosing

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these organs. A second peritoneal fold arises from the lesser curvature. This is the lesser

omentum. The lesser omentum will attach the stomach to the caudate lobe of the liver. The

stomach of Felis has the four basic mammalian portions. The first portion is the cardia that

receives food from the esophagus. Near the cardia is the fundus, a dome-shaped portion for

storing food. The bulk of the stomach is the body where mechanical and chemical digestion

occurs. The terminal portion is the pylorus which meets the small intestine at the pyloric

junction. You should cut a window in the body of the stomach along the greater curvature. You

will be able to see the rugae if the stomach is empty and should even be able to differentiate

some of the tunics.

Felis Digestive Organs 2

The intestines of amniotes are distinctly divided into a small intestine and large intestine.

The small intestine is very long and highly coiled. It is named for its relatively smaller bore

diameter. This allows for more contact between the digested food and the tunica mucosa of the

intestine which increases the efficacy of nutrient absorption. There are other modifications to the

small intestine that have evolved to maximize nutrient absorption. One of these can be observed

by cutting a window into the intestine. The inner aspect will be covered with numerous finger-

like extensions of the tunica mucosa called villi. Villi dramatically increase surface area to

increase nutrient absorption. The small intestine of mammals, birds, and some reptiles will be

divided into three segments. The first segment is the duodenum. It begins at the pyloric junction

and will have one lobe of the pancreas running partially along its length. The middle segment is

the jejunum. The last segment is the ileum which meets the large intestine at the ileocolic (or

ileocecal) junction. You will notice numerous lymph nodes around the ileum. This is to help to

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deal with pathogens that may have been ingested with food. Our appendix is a modification of

that. An extension of the intestinal tunica serosa called the mesentery will attach the small

intestine to the posterior abdominal wall and will attach its coils to one another.

The large intestine is shorter than the small intestine. It is named for its greater bore

diameter. Very little nutrient absorption occurs in the large intestine so contact between the

materials and the tunica mucosa is not as important. An extension of the colic tunica serosa,

called the mesocolon, will attach the large intestine to the posterior abdominal wall and will

attach its coils to one another. The large intestine has four principle portions: the cecum, the

colon, the rectum, and the anal canal. The cecum is a blind pocket located immediately below the

ileocolic junction. The ileocolic junction passes indigestible food into the first segment of the

colon, the ascending colon. The ascending colon will connect to the short transverse colon. The

transverse colon connects to the longest segment of the feline colon the descending colon. Most

mammals have only these three colic segments. Humans and apes have a fourth segment, the

sigmoid colon which empties into the rectum. In Felis the descending colon empties into the

rectum. It can be difficult to distinguish the descending colon from the rectum. One landmark is

the rim of the pelvis. The rectum begins below the rim of the pelvis. You will get a better view

of it and of the anal canal when you break the pelvis open for the urogenital system dissection.

The rectum serves for the storage of feces prior to elimination. The anal canal is a very short

segment that will most likely be constricted in your specimen. It serves to pass the feces out of

the body.

Felis Digestive System 3

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The accessory digestive organs of Felis include the liver, gall bladder, and pancreas. The

liver is more restricted in its location than was the case for Squalus or Necturus but is more

lobulated. It can be initially divided into a right and left portion. Running from the fissure that

divides these two portions is a peritoneal fold called the falciform ligament. The falciform

ligament attaches the liver to the diaphragm. The left portion of the liver is divided into the left

medial, left lateral, and caudate lobe (located at the lesser curvature of the stomach. The right

medial lobe dominates the right portion of the liver. This lobe contains the gall bladder and is

sometimes mistaken for two lobes. The right lateral lobe is along the posterior abdominal wall

and is divided into a cranial and caudal portion. The liver produces bile and bile salts for the

emulsification of fats. The spleen, like the liver, is a well-vascularized organ. Both will be a

rich brown color and the spleen can be confused for a lobe of the liver. The spleen is located

along the greater curvature of the stomach. It is an immune organ that serves as a reservoir for

blood. The liver is well vascularized because it processes nutrient-rich blood. The hepatic portal

system is a series of veins that drain nutrient-rich blood from the capillary beds of the stomach,

small intestine, and large intestine and carry it into the liver. The liver will screen pathogens,

remove poisons, and store various nutrients received from this blood.

Liver Left Medial Lobe Fundus Body Pancreas: Gastric Lobe Duodenal Lobe Spleen

Gall Bladder Liver Right Median Lobe Duodenum Descending Colon Rectum

Felis Digestive System 4

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The gall bladder is located in a depression, the cystic fossa, in the right medial lobe of the

liver. It will store bile produced by the liver. This bile will tend to give the gall bladder a

greenish hue. The gall bladder is drained by the cystic duct. The cystic duct meets with the right

and left hepatic ducts to form the common bile duct. The common bile duct will meet with the

main pancreatic duct to form the hepatopancreatic ampulla that brings bile and pancreatic juice

into the duodenum near the pyloric junction. You can observe the cystic, right hepatic duct, left

hepatic duct, and common bile duct by using your separating technique to remove the

surrounding peritoneum.

The pancreas is a lobulated glandular organ. In Felis it has two lobes. One lobe runs

along the greater curvature of the stomach and is sometimes referred to as the gastric lobe. The

other lobe runs a short distance along the duodenum and is sometimes called the duodenal lobe.

The two lobes are attached to each other (unlike the situation with Squalus). The pancreas

produces a variety of enzymes and buffering agents.

Part 3: Visceral Organs and Angiology

Part D: The Urogenital System

The urogenital system is actually two interrelated systems, the urinary and reproductive

systems. The kidneys are a nice example of ontogeny recapitulating phylogeny. The embryonic

kidney will go through a pronephric stage. The pronephric kidney will give rise to the

mesenephric kidney which is the adult kidney in Squalus and Necturus. In amniotes, such as

Felis, the metanephric kidney will replace the mesenephric kidney. All three types of kidneys

will work in close association with the blood vessels and will be well vascularized. The kidneys

will filter the blood and then modify this filtrate by removing substances from the blood (tubular

excretion) or from the filtrate (tubular resorption). Due to their development the kidneys will be

located against the musculature of the posterior abdominal wall or posterior pleuroperitoneal

wall. This will cause the kidneys to be dorsal to the parietal peritoneum, a situation termed

retroperitoneal. The ducts that drain the kidneys will be at least partially retroperitoneal as well.

Portions of the reproductive system will include the urinary system or have evolved from

urinary structures. For example, the mesenephric ducts of the mesenephric kidneys developed

into the vas deferens in amniotes. All three species will have two distinct genders. However, in

some cases the specimens may not have gone through puberty prior to being sacrificed. The

organs of these animals will be poorly developed. Typically your specimens will be sexually

mature adults but some of the Felis and Squalus specimens may not be. In some cases the uteri

of Felis and Squalus specimens will contain young. This range of developmental situations may

give you some valuable information depending on the range of specimens present in your lab.

Part D1: The Urogenital System in Squalus

In Squalus the urinary system consists of the paired mesenephric kidneys and

mesenephric ducts. The mesenephric kidneys run the length of the pleuroperitoneal cavity on the

dorsal wall. They flank the dorsal aorta and the paired posterior cardinal veins. In turn the renal

portal veins flank the mesenephros. The renal portal veins take blood rich in metabolic wastes

and deliver it into the afferent renal veins for processing by the mesenephros. The metabolites

will be removed from the blood stream and the blood will then enter into the posterior cardinal

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veins by way of the efferent renal veins. The resultant urine will drain into the mesenephric

ducts. The mesenephric ducts will drain into the cloaca. These structures are very fragile and

easily damaged. Once you have removed the parietal peritoneum there is nothing left to do. The

clarity of your specimen will be based more on the quality of vascular injections than on any

efforts of yours.

Squalus male Urogenital System

In Squalus the male gonads, the testes, are located at the cranial aspect of the

pleuroperitoneal cavity near the posterior cardinal sinuses. They will be held in place by a

peritoneal fold called the mesorchium. The testes secrete sperm into the mesenephric duct. As a

result, the mesenephric duct varies between sexually mature and immature sharks. The

mesenephric duct will be a straight tube in an immature individual and a convoluted tubule in a

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mature specimen. The caudal portion of the mesenephric duct will be expanded to give the

seminal vesicle. The seminal vesicles provide seminal fluid to the sperm. The caudal end of the

seminal vesicles will be further expanded to give the sperm sacs. Sperm will be stored in the

sperm sacs. During coitus the sperm will exit the sperm sacs and travel along a groove in the

clasper. The clasper will be inserted into the female cloaca to allow sperm to be introduced into

her urogenital system. You may notice a swollen structure immediately deep to the skin on the

ventral aspect of the clasper at its base. This is the siphon sac. The siphon sac draws in water to

aid in ejaculation during mating.

Squalus Male Urogenital System showing Testis

In female Squalus the gonads, the ovaries, are also located at the cranial aspect of the

pleuroperitoneal cavity near the posterior cardinal sinuses. They will be held in place by a

peritoneal fold called the mesovarium. The ovary will release ova into the oviduct (a.k.a; uterine

tube, fallopian tube). The oviduct begins at a funnel-shaped opening located immediately

posterior to the sinus venosus called the ostium. The oviducts develop from an embryonic tube

called the Muellerian Duct. So in females the mesenephric duct serves only as an excretory

structure. Along the oviduct will be the shell gland (a.k.a; nidamental gland). The shell gland is

located parallel to the caudal third of the ovary and will secrete a leathery shell around the

fertilized egg. The caudal portion of the oviducts will expand in a pregnant shark to become the

right and left uterus. Unlike mammals the chondrichthyan uteri do not unite. Both uteri open

separately into the cloaca. The uterus in a pregnant Squalus will contain numerous yolky eggs

(termed marcolethical) and several young. Young are borne ovoviparously after a gestation of

two years.

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Squalus Male Urogenital System showing Seminal Vesicle

(Note: The Sperm Sacs are immediately caudal to the seminal vesicles)

Ovary (containing ova) Oviduct Kidney Uterus Cloaca

Squalus Female Urogenital System in an Ovulating Specimen

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Part D2: The Urogenital System in Necturus

In Necturus the urinary system consists of the paired mesenephric kidneys and

mesenephric ducts. Unlike Squalus, however, the mesenephros do not run the length of the

pleuroperitoneal cavity. Instead they are caudally oriented. This condition leads too the kidneys

of certain jawed fishes and amphibians to be termed opisthonephros meaning “rear facing

kidney”. The kidneys will flank the dorsal aorta and post cava. The renal portal veins will flank

the kidneys. The kidneys taper cranially. Along the lateral margin will be the mesenephric ducts

which open into the cloaca. The cloaca will have an expansion termed the urinary bladder.

However, this structure is not a true bladder and is not homologous to the mammalian urinary

bladder. The kidneys will be easier to see in males since in females the ovaries obscure much of

the surrounding area, especially in ovulating specimens.

Necturus Male Urogenital System

In male Necturus the testes will be located immediately lateral to the middle aspect of the

mesenephros. They are actually embedded within the parietal peritoneum, a condition termed

“intraperitoneal” and held in place by the mesorchium. Numerous tiny white tubules run through

the mesorchium called the efferent ductules. The efferent ductules carry sperm into the kidney, in

particular into the mesenephric duct. As was the case with Squalus, the mesenephric ducts are

both excretory and reproductive structures in males. In a sexually mature Necturus the

mesenephric ducts will be convoluted along the cranial two thirds. Sperm will be carried along

the mesenephric ducts for release into the environment by way of the cloaca. Necturus practice

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external fertilization. Males will have a swollen region external to the cloaca called the cloacal

gland. This gland produces secretions used in mating.

Necturus Female Urogenital System

(Note: the numerous large eggs are obscuring many structures)

In female Necturus the ovaries will also be located immediately lateral to the middle

aspect of the mesenephros. They are held in place by the mesovarium. When producing ova the

ovaries can become quite large and heavy with eggs. In this condition they will obscure many

lower pleuroperitoneal features. The mesenephric ducts in females are solely excretory n

function and will remain straight throughout life. The reproductive ducts, as is the case with

Squalus, are the oviducts that developed from Muellerian ducts. They will be large convoluted

tubules in a female producing eggs. The oviducts begin at the funnel-shaped ostium, one per

oviduct, located at the cranial aspect of the pleuroperitoneal cavity. The ostium has cilia. Ciliary

beating will draw the ovulated ova into the ostium and oviduct. Along the length of the oviducts

will be numerous glandular evaginations to produce the “jelly” typical of amphibian eggs. The

oviducts terminate at the cloaca. The terminal portion of the oviducts will be expanded and will

store eggs prior to copulation. These terminal expansions are termed uteri by some but are not

considered to be true uteri by most comparative anatomists. While the female is embraced by a

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male (amplexus), the eggs will be released into the water. The male will be releasing his

spermatozoa simultaneously for external fertilization.

Part D3: The Urogenital System in Felis

In Felis the urinary system consists of the paired metanephric kidneys, the ureters, the

urinary bladder, and the urethra. The kidneys in amniotes are much more compact than are those

of other vertebrates. As is the case for all vertebrate kidneys, the metanephric kidney is

retroperitoneal. Three tissue layers that will also be retroperitoneal will surround it. The first

layer in the renal fascia. This is a layer of connective tissue that anchors the kidney to other

structures. The second layer is a layer of adipose tissue called the adipose capsule. The adipose

capsule serves to protect the kidneys from mechanical trauma. Depending on the amount of fat

in your specimen as a whole, there can be a good amount of adipose in the adipose capsule. Care

should be taken to remove this adipose since there are a number of blood vessels and structures

embedded within it. These structures include the ureters and the adrenal glands. The ureters will

be white, as is the adipose, and can easily be removed with the fat. The adrenal glands are small,

beige endocrine organs located cranial to the kidneys. Due to their small size they also are easily

lost. Use your fine tip scissors and separating technique to break the fat away. The deepest layer

is the renal capsule, a thin layer of fibrous connective tissue that covers the external surface of

the kidney.

Descending Colon Abdominal Aorta Posterior Vena Cava Renal Vein & Artery

Urinary Bladder Ureter Hilus Kidney

Felis Urinary System

When the kidney is unveiled you will notice that it is a bean-shaped organ with a

depression on its medial aspect. That depression is termed the hilus. The hilus is where the renal

artery enters the kidney and the renal vein and ureter exit the kidney. To observe the internal

structure of the kidney you will need to slice it open using your scalpel. Begin your incision on

the convex lateral surface and bring it through to the hilus. Do not cut into the hilus. If the

technique is performed properly the kidney will open and close like a book and the hilus will

serve as the binding of the book. Once you have opened the kidney you will be able to observe a

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number of features. Gently peel away the renal capsule. The interior of the kidney will have

three differently colored zones. The outermost zone, which is typically a grayish hue, is the

renal cortex. The middle, brownish zone, is the renal medulla. You may notice that the border

between the cortex and medulla has a scalloped appearance. Each of these crescents is the base

of a renal pyramid. The renal pyramids are subunits of the renal medulla. The innermost, ivory

colored zone is the renal pelvis. The flap-like medullary structure projecting into the pelvis is

the renal papilla. The renal pelvis drains urine from the renal medulla. The renal pelvis

resembles the ureter since they are actually composed of the same tissues and developed from an

out branching of the mesenephric duct. The renal medulla and cortex are histologically and

developmentally distinct from the renal pelvis. During development the ureter and renal pelvis

invaded the nephrogenic mesoderm that produces the medulla and cortex of the metanephros.

You may also notice blood vessels throughout the kidney. The kidneys are extremely well

vascularized structures since they remove wastes from the blood stream.

Renal Papilla Renal Pelvis Base of a Renal Pyramid

Renal Capsule Renal Cortex Renal Medulla

Felis Internal Structure of the Kidney

The ureters are paired structures that carry urine from the kidney to the urinary pelvis.

The ureters are retroperitoneal along most of their length. However, the terminal portion

penetrates the parietal peritoneum to enter the pelvis and to drain into the urinary bladder. The

urinary bladders of placental and marsupial mammals are considered to be true bladders. Unlike

other “false bladders” they receive urine directly from the ureters and develop from the allantois,

an embryonic membrane. The ureters will enter the bladder from the caudal-dorsal border. This

allows the bladder more room for distension. The bladder is a muscular organ. If the urinary

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bladder of your specimen is flaccid and stretched it will be empty. An empty bladder is safe to

cut open. Make an incision along the cranial border of the bladder. You should be able to see

that the internal structure is arranged into folds called rugae to allow for distension. You should

also be able to see the openings of three vessels, the two ureters and the one urethra, on the floor

of the urinary bladder. This feature is called the trigone of the bladder. If the bladder is a hard,

acorn-like structure it contains urine. It is advised that you do not make an incision into a

urinary bladder in this state.

Marsupial and placental mammals lack a cloaca. As a result, the true bladder can not

empty into a cloaca. Instead it empties into a tubular organ called the urethra. The urethra serves

to drain the bladder and to release waste into the external environment. In females the urethra is

a solely excretory organ while the urethra of males is both excretory and reproductive. As a

result the urethra will differ between the two genders. In females the urethra is a short organ. In

males the urethra will pass through the intromittent organ, the penis, and will necessarily be

longer. The male urethra will have three segments. The first segment to receive urine is situated

immediately below the urinary bladder. This segment will be surrounded by the prostate gland

and is called the prostatic urethra. Between the bladder proper and the prostatic urethra in Felis

is a narrow portion called the neck of the bladder. Although this is considered to be a portion of

the urinary bladder it is really a portion of the prostatic urethra. The prostatic urethra drains into

a short segment that penetrates the floor of the pelvis called the membranous urethra. The

membranous urethra drains into the longest segment called the penile urethra (a.k.a.; spongy

urethra) that passes through the length of the penis.

Felis Female Urogenital Organs

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In mammals the structures of the female reproductive system will give rise to the

structures of the male reproductive system. For that reason we will begin with the female

reproductive system in Felis. The female reproductive system in mammals consists of a pair of

ovaries, a pair of oviducts, a singular uterus, and a singular vagina. The ovary is the female

gonad. It will be located in the lower abdominal cavity in Felis. It will be held in place by

peritoneal folds such as the suspensory ligament. On occasion you will be able to observe a

bulge on the surface of the ovary. This bulge is an ovum that was about to enter ovulation. The

oviduct is a tubular organ found on the lateral margin of the ovary. The oviduct serves to

transport the ovum/embryo to the uterus and also serves as the sight of fertilization. It has three

sections. The first section is the infundibulum. The infundibulum is a funnel-shaped opening and

will have extensions called fimbriae to increase surface area for capturing the ovulated ovum.

The middle and longest segment is the ampulla. The last segment is the isthmus, a narrow

portion that enters the uterus at the apex of the cornu.

Urethra Vagina Urinary Bladder Uterine Body Uterine Cornu Rectum

Felis Lower Female Urogenital System

Placental mammalian uteri come in two forms: simplex and bicornuate. The uterus of

Felis is bicornuate. It is composed of a right and left uterine horn (a.k.a.; uterine cornu) and the

uterine body. The uterine horns are held in place by peritoneal folds such as the broad ligament

and the round ligament. They will be located in the lateral aspect of the lower abdominal cavity.

Their size and width will be dependent on the reproductive state of your specimen. In a pregnant

animal the uterine horns can be quite large. The embryos and fetuses reside in the uterine horns.

They enter the uterine body only during parturition. The two uterine horns meet caudally at the

uterine body. To observe the uterine body, and other pelvic structures, you will need to open the

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pelvis. Take your scalpel and make an incision through the muscles superficial to the pubic

symphysis. While doing this, exert pressure on the knees with your other hand. In a smaller

specimen this may be enough to open the pelvis. If it is not then take the bone clippers and cut

through the pubic symphysis. The pelvis will contain some adipose tissue that may be removed

through the separating technique. The body of the uterus will meet the vagina. Unless the

specimen is in the later stages of pregnancy the transition may be hard to recognize. The vagina

will be situated between the urethra (ventral) and rectum and anal canal (dorsal). It is a muscular,

tubular organ that will open into the urogenital vestibule.

Felis Male Urogenital System 1

The male reproductive system in mammals consists of a pair of testes, the scrotum, a

paired duct system, the penis, and a number of accessory sex glands. The testis is the male

gonad and will produce spermatozoa and male sex hormones. These organs are homologous to

the ovaries. To allow for spermatogenesis in mammals the testes must be kept at a temperature

that is slightly lower than is the internal core temperature of the animal. As a result, the testes

are held outside of the body in a cutaneous outpocketing called the scrotum. The amount of time

that the testes spend in the scrotum varies based on the reproductive strategy of the species. The

testes will reside in the scrotum only temporarily in mammals with set breeding seasons. In

species such as Felis and humans that are always reproductively active the testes reside in the

scrotum permanently. Using your scissors open one side of the scrotum, only one scrotal sac, to

expose one testis. The scrotum is homologous to the labia majora and labia minora of the female

vulva. The passageway between the scrotum and pelvic cavity is the inguinal canal. The testes

are held in place by collagen bundles.

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Felis Male Urogenital System Focusing on the Duct System

Sperm will be released into a series of ducts. The testis itself has numerous convoluted

tubules called seminiferous tubules that serve as the site of gametogenesis. The testes are

drained by the epididymis. The epididymides are comma-shaped organs located on the lateral

margin of the testes. The epididymis has three portions: head, body, and tail. The head is the

widest portion. It is located on the superior aspect of the testis and contains the efferent ductules

that receive sperm from the testis. The epididymis tapers from the head into a body and a

narrowing tail. The body and tail contain the ductus epididymis. The tail of the epididymis

connects to the vas deferens (a.k.a.; ductus deferens). The vas deferens will carry sperm from

the scrotum into the pelvis and to the urethra. Along a portion of its length the vas deferens runs

with other organs in a composite structure called the spermatic cord. The spermatic cord

includes the vas deferens, testicular artery, testicular vein, testicular lymphatic, and testicular

nerve. All are covered by a connective tissue sheath and by the cremaster muscle (which is an

outgrowth of the rectus abdominis). The cremaster will allow the testes to be pulled closer to the

pelvis as required by ambient temperatures. You can observe the spermatic cord separating into

its composite structures once it enters the pelvis through the inguinal canal. The blood vessels

will travel cranially towards their branching points while the vas deferens will loop behind the

bladder. To observe the entrance of the vas deferens into the urethra, and other pelvic structures,

you will need to open the pelvis. The spermatic cords will most likely still be along the midline,

over the pubic symphysis and partially embedded in adipose. Use your fine tip scissors to

separate the two spermatic cords from one another and from the pubic symphysis. Next take your

scalpel and make an incision through the muscles superficial to the pubic symphysis. While

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doing this, exert pressure on the knees with your other hand. In a smaller specimen this may be

enough to open the pelvis. If it is not then take the bone clippers and cut through the pubic

symphysis. The pelvis will contain some adipose tissue that may be removed through the

separating technique.

Neck of Bladder Prostate Urethra Penis: Crus Shaft Glans Prepuce (cut)

Urinary Bladder Spermatic Cord Epididymis: Head Body Tail Testis

Felis Male Urogenital System 2

The two vas deferens enter the urethra at the prostate. The prostate will appear as a slight

swelling surrounding a portion of the urethra. The size will correspond to whether or not your

specimen was of reproductive maturity when it was sacrificed. The prostate is an accessory male

sex gland that contributes to seminal fluid. It will also engorge with blood during the sexual

response to cause the urethra to be only a reproductive structure during mating. This is

necessary since the pH of urine will kill the spermatozoa. The prostate is homologous to the

uterus. The ejaculate (spermatozoa plus seminal fluid) will pass through the urethra to exit at the

urethral aperture at the distal extent of the glans penis. The penis is the intromittent organ of

mammals. It has three regions that can be observed through your dissection. The angle between

the membranous urethra and the base of the penis is termed the crus of the penis. Most of the

length of the penis is termed the shaft of the penis. It will terminate in a distal, expanded portion

called the glans penis. The glans penis is homologous to the clitoris of the female vulva. You

will notice that the dorsal surface of the glans penis will have numerous keratinized, spike-like

structures to aid in coitus. A fold of skin termed the prepuce will cover the glans penis. To

expose the penis you will need to cut through the prepuce. You can do this by pulling up on the

prepuce while inserting your scissors into the opening and using your separating technique until

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the tip of the glans is exposed. Now you can safely use your scissors to cut through the dorsal

aspect of the prepuce. This will expose the length of the penis.

Part 3: Visceral Organs and Angiology

Part E: The Circulatory System

The circulatory system of vertebrates consists of blood, blood vessels, and a

muscular, pumping heart. Blood vessels are hollow organs that serve to carry blood throughout

the body. Their walls are composed of tissue layers called “tunics”. The innermost is the tunica

intima/tunica interna which is in direct contact with the blood. The second, middle, tunic is the

tunica media. The outermost tunic is the tunic externa/tunica adventitia. There are three classes

of blood vessels: arteries, veins, and capillaries. Arteries serve to carry blood from the heart to

the tissues of the body. Since they are carrying blood at its highest pressure, arteries have

proportionately the thickest walls with the tunica media being very thick. Capillaries are

microscopic blood vessels where materials are exchanged between the tissues and the blood. To

facilitate this, capillaries are very thin walled to maximize diffusion. They are microscopically

small and will not be a feature of your dissection. Veins serve to carry blood back to the heart

from the body’s tissues. Their walls are proportionately thinner than are those of arteries since

they carry blood at a lower pressure. Also, due to the lower pressure, veins will have numerous

valves projecting into the lumen to prevent the backflow of blood.

The heart is a muscular pump. It is located in the pericardial cavity and covered by a

serous membrane called the pericardium. The heart evolved from blood vessels. As a result, the

heart wall is composed of three tissue layers that are similar to the three tunics of large blood

vessels. The inner lining is termed the endocardium. The middle and thickest layer is the

myocardium. It is rich in cardiac muscle tissue to pump the blood. The epicardium is the outer

layer of the heart. The heart wall will receive its own blood supply through the coronary blood

vessels. Vertebrate hearts can be divided into single circuit and double circuit hearts. Single

circuit hearts are found in fishes. Blood passes form the heart to the gills, from the gills to the

rest of the body, and from the rest of the body back to the heart. Blood picks up oxygen from the

gills and delivers it to the rest of the body where the cells will use the oxygen for respiration.

The deoxygenated blood will then be returned to the heart. Double circuit hearts are found in

amniotes. There are two currents or circuits. One is the pulmonary circuit which carries

deoxygenated blood from the heart to the lungs to pick up oxygen. The oxygenated blood is then

carried from the lungs back to the heart. The other is the systemic circuit which carries

oxygenated blood from the heart to all of the tissues of the body. There oxygen is used for

respiration and carbon dioxide is dumped into the blood. The deoxygenated blood is returned to

the heart.

Part E1: The Circulatory System in Squalus

The heart of Squalus is typical for that of most fishes. It has four portions (in sequence of

receiving blood): sinus venosus, atrium, ventricle and conus arteriosus. Fish are said to have a

two-chambered heart, one atrium and one ventricle. The sinus venosus receives deoxygenated

blood from the body’s tissues. It is a thin walled vein having little muscle and being composed

mostly of fibrous connective tissue. The sinus venosus primarily serves to collect deoxygenated

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Arteries of the Squalus Oropharynx

1. Internal Carotid Artery 2. Hyoidean Epibranchial Artery 3. Radix Aorta

4. Vertebral Artery 5-8 Efferent Branchial Arteries (I-IV) 9. Esophageal Artery

10. Dorsal Aorta

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Squalus Arteries

1. Dorsal Aorta 2. Celiac 3. Gastrohepatic 4. Gastric

5. Hepatic 6. Pancreaticomesenteric 7. Intraintestinal 8. Duodenal

9. Pyloric 10. Anterior Intestinal 11. Gastrosplenic 12. Posterior Intestinal

13. Posterior Mesenteric 14. Iliac 15. Femoral 16. Caudal

17. Annular

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Squalus Veins

1. Lateral Abdominal 2. Renal Portal 3. Posterior Cardinal 4. Dorsal Aorta

5. Hepatic Portal 6. Gastric 7. Leinomesenteric 8.Posterior Intestinal

9. Posterior Splenic 10. Pancreaticomesenteric 11. Pyloric 12. Intraintestinal

13. Anterior Splenic 14. Anterior Intestinal 15. Annular

Note: Systemic veins are in blue and veins of the hepatic portal system are in yellow.

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Squalus Deep Vessels & Heart

1. Afferent Branchial a. 2. Ventral Aorta 3. Conus Arteriosus 4. Ventricle

5. Atrium 6. Sinus Venosus 7. Internal Jugular v. 8. External Jugular v.

9. Subclavian v. 10. Brachial v. 11. Lateral Abdominal v. 12. Posterior Cardinal Sinus

13. Genital Sinus 14. Dorsal Aorta 15. Posterior Cardinal v. 16. Renal Portal v.

17. Afferent renal v. 18. Efferent renal v. 19. Cloacal 20. Iliac

21. Femoral 22. Caudal a. 23. Caudal v. 24. Common Cardinal v.

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blood from the tissues of the body and has little contractile action. (Blood is pulled into the sinus

venosus due to pressure caused by ventricular contractions.) Blood travels from the sinus

venosus, through the sinoatrial aperture, into the atrium. A pair of unidirectional valves guards

the sinoatrial aperture. These valves prevent the backflow of blood. Blood moves into the atrium

when it relaxes after emptying (systole). The atrium receives blood from the sinus venosus and

pushes it into the ventricle. This chamber is a thin walled muscular sack. Contractions of its

muscular component will push the blood through the atrioventicular aperture into the ventricle.

The atrioventicular aperture is also guarded by a pair of unidirectional valves which also prevent

the backflow of blood. The ventricle is a muscular, thick walled chamber that serves as the main

pumping chamber of the heart. It pumps blood into the conus arteriosus. The ventricle generates

the main force for fish circulation. The conus arteriosus receives blood from the ventricle and

conducts it to the gills by way of the ventral aorta. The conus arteriosus extends to the cranial

most extent of the pericardial chamber and joins with the ventral aorta. The wall of the conus

arteriosus is primarily composed of cardiac muscle and elastic connective tissue. The cardiac

muscle component of the conus arteriosus allows for steady blood pressure in the ventral aorta. It

also has a series of semilunar valves to prevent the backflow of blood into the ventricle. The

conus arteriosus is different between cartilaginous and bony fishes. Cartilaginous fishes, such as

Squalus, have a relatively longer conus arteriosus. Bony fishes, particularly teleosts, have a

shorter conus arteriosus. Since the conus arteriosus is shorter it has a muscular swelling at it s

base to compensate called the bulbus arteriosus.

Squalus Heart

The arteries serve to carry blood from the heart to the tissues of the body. Typically this

blood will be oxygenated but that is not always the case. In fishes, such as Squalus, arterial flow

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begins with the ventral aorta receiving blood from the conus arteriosus and bringing it to the

gills. This blood is deoxygenated. Capillary beds in the gills will serve as the site of gas

exchange. The oxygenated blood will be recovered by the dorsal aorta and delivered to the

throughout the body. During development the ventral aorta extends craniad, under the pharynx,

and connects with the developing aortic arches. In the primitive gnathostome condition there

were six pairs of aortic arched connecting the ventral aorta and dorsal aorta. The first aortic

arches to develop are those of the mandibular arch. The other five arches develop shortly after.

However, before the sixth pair fully forms, the first pair will disappear leaving only branches

called the spiracular arteries. The second pair will sprout buds that will develop into the first

pretrematic arteries. Other buds will sprout off of the third through sixth pairs of aortic arches.

These buds will become the posttrematic arteries. The posttrematic arteries will give rise to

branches that will become the other pretrematic arteries. Soon during development arches 2

through 6 will develop occlusions where portions of the vessel will be lost. Segments located

ventral to the occlusions will give rise to the afferent branchial arteries while the segments

located dorsal to the occlusions will give rise to the efferent branchial arteries. At the same time

capillary beds will begin to form in the demibranchs. These capillary beds are special in that

they are drained by arterioles instead of venules (which is the typical condition). They are an

example of a rete mirabilia.

Esophageal A. Radix Aorta (poorly injected) Mock up of a Radix Aorta

Efferent Branchial Arteries Hyoidean Epibranchial A. Internal Carotid A.

Squalus Arteries of the Doral Oropharynx

In your dissection you should be able to observe the ventral aorta passing through the

floor of the oropharynx and branching into four pairs of afferent arteries going to the gills. These

structures tend to be poorly injected and will be hard to find. However, the roof of the

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oropharynx will be fairly well injected and you should be able to observe its arteries. There will

be four pairs of efferent branchial arteries receiving oxygenated blood from the gills. They will

drain into the dorsal aorta that can be observed dorsal to the pleuroperitoneal cavity and at the

caudalmost extent of the oropharynx. The anterior extensions of the dorsal aorta are the paired

radix aortae (which are sometimes referred to as the “paired dorsal aortae”). They are small “L-

shaped” vessels located anterior to the first pair of efferent branchial arteries and immediately

lateral to the vertebrae. Immediately medial to these arteries are the difficult to find vertebral

arteries. Extending anteriorly from each first efferent artery will be a small artery that receives

blood directly from the first gill pair. This is the hyoidean epibranchial artery. The hyoidean

epibranchial artery will extend anteriorly along the roof of the oropharynx. Part way along its

length it will meet with the radix aorta. At its anterior extent it will branch into the stapedial

artery (which services the extrinsic ocular muscles) and the internal carotid artery. Coming off

of the second efferent branchial artery and extending caudally will be a wavy artery called the

esophageal artery. The subclavian arteries will arise from the dorsal aorta between the third and

fourth efferent branchials and will extend towards the pectoral fins. One of its branches will be

the brachial artery of the pectoral fin. Another will be the lateral artery that runs along the lateral

line and lateral abdominal vein. The vein is easy to find but the artery typically injects poorly.

Squalus Early Branches of the Dorsal Aorta

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Celiac Trunk Gastrohepatic A. Gastric A. Posterior Intestinal A. Gastrosplenic A.

Hepatic A. Pancreaticomesenteric A. Anterior Intestinal A.

Squalus Visceral Arteries 1

The dorsal aorta will extend through the pleuroperitoneal cavity immediately ventral to the

vertebral column. It will give rise to the visceral arteries. The first branch will be the celiac

artery. This is a prominent artery that will divide into two branches: the gastrohepatic artery and

the pancreaticomesenteric artery. The gastrohepatic artery is a short vessel that will divide into

the gastric artery, to service the stomach, and the hepatic artery, to service the liver. The

pancreaticomesenteric artery gives rise to numerous conduits. One easily identified artery is the

anterior intestinal artery. The anterior intestinal will travel along the ventral wall of the intestine

and give rise to numerous annular arteries which run near the folds of the spiral valve. At the

point where the anterior intestinal arises three other vessels will also arise. One will enter into the

pyloric region of the stomach and is the pyloric artery. The second will be the duodenal artery

supplying a small portion of the intestine prior to the spiral valves. The third is the intraintestinal

artery which extends through the spiral valve. The second branch coming off of the dorsal aorta

is the posterior intestinal artery. It will enter the dorsal wall of the intestine. It will also give rise

to numerous annular arteries which will fuse to those that arose from the anterior intestinal

artery. Branching close to the posterior intestinal artery will be the gastrosplenic artery. The

gastrosplenic artery will enter into the spleen and traveling through the spleen will also send

branches into the stomach. In some specimens the posterior intestinal and gastrosplenic arteries

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Pyloric A. Anterior Intestinal A. Annular Arteries Posterior Mesenteric A.

Gastrosplenic A. Posterior Intestinal A. Dorsal Aorta (poorly injected)

Squalus Visceral Arteries 2

Squalus Left Iliac Artery

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arise from a common vessel that branches off of the dorsal aorta called the anterior mesenteric

artery. Typically the fourth major artery arising from the dorsal aorta will be the posterior

mesenteric which will service the rectal gland. Near the cloaca the dorsal aorta will branch into

the paired iliac arteries and caudal artery. The iliac arteries run into the pelvic fins and give rise

to the femoral arteries. The caudal artery runs through the tail and caudal fin.

Veins will drain blood from capillary beds. In a triple-injected specimen the veins will

have two colors. Yellow vessels designate veins of the hepatic portal system. The hepatic portal

system is a series of veins draining nutrient-rich blood from the digestive tract and carrying it to

the liver for processing. Blue vessels designate systemic veins. Systemic veins usually convey

blood that is high in carbon dioxide and other metabolic wastes to the heart and, subsequently,

the gills. The systemic vessels will also contain the renal portal system. This venous pathway

carries blood high in muscle waste products from the tail to the kidneys for cleansing. On

occasion an error with specimen processing may cause the colors to be reversed.

Hepatic Portal Vein Gastric V. Anterior Splenic V. Posterior Splenic V.

Pancreaticomesenteric V. Annular V. Anterior Intestinal V.

Squalus Hepatic Portal System 1

The largest vein of the hepatic portal system is the hepatic portal vein. It will run along

the common bile duct and the hepatic artery. It drains three veins: the gastric vein, the

pancreaticomesenteric vein, and the lienomesenteric vein. The gastric vein drains the capillary

beds of the stomach and will run along the gastric artery. The pancreaticomesenteric and

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lienomesenteric veins are easy to confuse at first since they both run near each other and towards

the intestines. However, the pancreaticomesenteric vein runs with the pancreaticomesenteric

artery while the lienomesenteric vein runs through the dorsal lobe of the pancreas. The

pancreaticomesenteric vein has many of the same branches that you saw with the

pancreaticomesenteric artery. There is an anterior intestinal vein which is on the ventral aspect of

the intestine (parallel to the anterior intestinal artery) and will drain the ventral portions o the

annular veins. There is also a pyloric vein, draining the pyloric stomach, and an intraintestinal

vein, draining the spiral valves. The pancreaticomesenteric vein will also drain the anterior

splenic vein. The anterior splenic vein is a smaller vein running through the peritoneum along the

pyloric portion of the greater gastric curvature and draining the spleen. It is easy to lose when

removing the peritoneum. The lienomesenteric vein drains two fairly easily found veins: the

posterior intestinal vein and the posterior splenic vein. The posterior intestinal vein runs along

the dorsal aspect of the intestines (parallel to the posterior intestinal artery) and drains the

posterior portions of the annular veins. The posterior splenic vein will drain the caudal portion

of the spleen and typically runs parallel to the gastrosplenic artery.

Squalus Hepatic Portal System 2

The systematic veins anterior to the pleuroperitoneal cavity will not be injected and hard

to find at best. However, many systematic veins in the pleuroperitoneal cavity should be fairly

well injected and easier to work with. The renal portal system of the systemic vessels begins with

the caudal vein carrying blood from the tail into the pleuroperitoneal cavity. The caudal vein

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feeds into the right and left renal portal veins. The renal portal veins run along, and immediately

lateral to, the mesenephric kidneys. Numerous small veins will branch off of the renal portal

vein and enter into the kidney. These are the afferent renal veins. The afferent renal veins

deliver the blood to the kidneys for the removal of metabolic wastes, excepting carbon dioxide.

(The tail is the main locomotory structure for swimming in sharks and the muscles will produce a

good deal of waste.) The blood will be processed by the kidneys and will then drain into a series

of small vessels called efferent renal veins. The afferent renal veins are on the lateral half of the

kidney and the efferent renal veins are on the medial half of the kidney. These vessels will drain

into the paired posterior cardinal veins. The posterior cardinal veins are located medial to the

mesenephros and immediately lateral to the dorsal aorta. These paired vessels will carry the

blood cranially to large venous sinuses. These are the right and left posterior cardinal sinuses. A

sinus is a thin walled but large vein and so the posterior cardinal sinuses are fragile. They will be

located behind the liver, near the gonads, in the cranial one fifth of the pleuroperitoneal cavity.

Immediately caudal to the posterior cardinal sinus, and draining into it, is the genital sinus. In

most specimens it will be difficult to differentiate the genital sinus from the posterior cardinal

sinus. The right and left posterior cardinal sinus will drain into the right and left common

cardinal veins respectively. The common cardinal veins will return blood to the heart by feeding

blood into the sinus venosus. Afferent Renal V.

Squalus Renal Portal System

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Squalus Pleuroperitoneal Vessels

The femoral vein can be observed by separating the pelvic depressor muscles. It will

drain into the iliac vein which will run parallel to the iliac artery and drains into the lateral

abdominal vein. The lateral abdominal veins will receive blood from veins of the lateral wall

myomeres. In addition, the right and left lateral abdominal veins will both drain the cloacal

veins. The cloacal veins enter into the lateral abdominal vein at the same point as the iliac veins.

The lateral abdominal vein will run through the lateral body wall near to the lateral line and

lateral abdominal artery and will carry blood cranially. At the pectoral girdle it will drain the

subclavian vein. The subclavian vein carries blood from the brachial vein of the pectoral fin. At

its most cranial extent the lateral abdominal vein will drain into the common cardinal vein. The

common cardinal veins will return blood to the heart from all of the systematic vessels. It drains

the lateral abdominal, anterior cardinal, internal jugular veins and the posterior cardinal sinus.

Unfortunately it is usually difficult to observe this important vessel due to its location deep to the

coracoid bar and its fragility.

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Squalus Showing the Right Posterior Cardinal Sinus

Part E2: The Circulatory System in Necturus

The heart of Necturus, like most amphibians, will display modifications due to aerial

respiration. These modifications allow oxygenated blood returning from the lungs or swim

bladder to be separated in the heart from deoxygenated blood returning from the other organs.

There are typically four modifications in the amphibian heart over that of gill breathing fishes.

One modification was the establishment of a complete or partial interatrial septum. This

establishes either the complete or partial separation of a right and left atrium. The interatrial

septum is complete in anurans and some urodeles. The septum is lacking in lungless urodeles. It

will be partial in Necturus although they do not use the lungs for respiration. In most species the

veins for the swimbladder/lung empty into the left atrium. So this blood will be oxygenated.

Deoxygenated blood enters the right atrium by way of the sinus venosus. Another modification

was the establishment of a partial interventricular septum or of ventricular trabeculae. Both

structures serve to separate oxygenated and deoxygenated blood. Necturus will possess a partial

interventricular septum. A third modification was the establishment of a spiral valve in the conus

arteriosus. The spiral valve also serves to separate oxygenated and deoxygenated blood.

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It forces oxygenated blood into the aortic arches that go to the tissues. It also forces

deoxygenated blood into the aortic arches that go to the lungs or gills. Urodeles, such as

Necturus, lack the spiral valve. The fourth modification is the shortening of the ventral aorta to

point where it is virtually nonexistent. As a result blood goes directly from the conus arteriosus

to the appropriate vessel. Necturus, and urodeles in general, are the exception and have a

prominent ventral aorta.

Bulbous Arteriosus Left Atrium Parietal Pericardium

Right Atrium Conus Arteriosus Ventricle

Necturus Superficial Heart

The Necturus heart possesses two atria and one ventricle. It is sometimes referred to as a

“three chambered heart”. Atria are relatively thin walled structures that receive blood from veins

The right atrium receives deoxygenated blood from all of the tissues of the body by way of the

sinus venosus. The sinus venosus is a thin walled vessel located dorsal to the heart. A valve, the

sinoatrial valve, guards the opening between the sinus venosus and the right atrium. The left

atrium receives oxygenated blood from the gills by way of the pulmonary trunk. The two atria

are separated by a partial interatrial septum. Both atria will send blood into the ventricle.

However, the oxygenated and deoxygenated blood will be incompletely segregated by a partial

interventricular septum. The ventricular wall is more muscular, and thicker, than is that of the

atria. A pair of valves, the right and left atrioventricular valves (or AV valves), prevents the

backflow of blood between the ventricle and the two atria. The ventricle will send blood into the

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Necturus Arteries & Heart

1. Bulbus Arteriiosus 2. Conus Arteriosus 3. R. Atrium 4. L. Atrium

5. Ventricle 6. External Carotid 7. Internal Carotid 8. Vertebral

9. Branchials 10. Radix Aorta 11. Subclavian 12. Pulmonary

13. Cutaneous 14. Axillary 15. Brachial 16. Segmentals

17. Dorsal Aorta 18. Gastric 19. Celiacomesenteric

20. Pancreaticoduodenal 21. Hepatic 22. Splenic 23. Mesenterics

24. Intestinals 25. Genitals 26. Renals 27. Iliac

28. Femoral 29. Caudal 30. Hypogastric

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Necturus Veins

1. Common Cardinal 2. Subclavian 3. Brachial 4. Posterior Cardinal

5. Pulmonary 6. Post Cava 7. Genital 8. Renal

9. Renal Portal 10. Pelvic 11. Iliac 12. Femoral

13. caudal 14. Ventral Abdominal 15. Mesenteric 16. Intestinals

17. Hepatic Portal 18. Gastrosplenic 19. Splenic 20. Gastric

Note: Systemic veins are in blue and veins of the hepatic portal system are in yellow.

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conus arteriosus. This artery will have numerous semilunar valves to prevent blood from flowing

backwards. The conus arteriosus in teleosts and amphibians are relatively shorter than was that

of Squalus. To compensate for this the conus arteriosus has a swollen, muscular structure called

the bulbous arteriosus which will help to propel the blood out of the pericardial cavity.

Efferent Common Trunk External Carotid A. Internal Carotid A. Radix Aorta Dorsal Aorta

Necturus Blood Vessels of the Head

The conus arteriosus will primarily send deoxygenated blood into the ventral aorta. The

ventral aorta is relatively long in urodeles such as Necturus for amphibians. It will carry blood

cranially and will branch into a right and left trunk that will immediately branch into an anterior

first afferent artery and a larger common (afferent) trunk. In turn the right and left common

trunks will branch into the second and third afferent branchial arteries on each side. The afferent

branchial arteries will bring oxygen-poor blood to the gills. The vasculature will ramify into

smaller arteries and capillary beds to allow for an exchange of gases. The oxygenated blood will

travel into anastomizing vessels that will coalesce into the three pairs of efferent branchial

arteries. The first efferent branchial artery will send off a branch that will service the floor of the

mouth called the external carotid artery. It will also send off a second, more medial, branch that

will service the roof of the mouth called the internal carotid artery. The second and third efferent

branchial arteries will join to form a second, efferent, common trunk. Where the second and

third efferent arteries join at the efferent common trunk another artery arises. This is the

pulmonary artery. The right and left pulmonary arteries will travel to the lungs and can be seen

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on the dorsal pulmonary surface. The pulmonary arteries are the remains of the sixth aortic arch.

A pair of radix aortae will arise from the fusion of the efferent common trunk with the first

efferent artery on each side. These “L-shaped” paired arteries will fuse caudally, near the

pericardial cavity, to form the singular dorsal aorta. The dorsal aorta will carry blood the length

of the body and into the tail where it becomes the caudal artery.

Necturus Visceral Blood Vessels 1

The dorsal aorta runs immediately ventral to the vertebral column. It will branch into the

paired subclavian arteries in the pectoral region. The subclavian artery will exit the body wall

and become the axillary artery. The axillary artery will give rise to the brachial artery that runs

along the humerus. Pairs of arteries will arise segmentally from the dorsal aorta and run into the

lateral body wall. These are the parietal arteries. They will be located internal to the myosepta.

The first visceral branch to arise from the dorsal aorta is the gastric artery. This vessel will

service the stomach. The next visceral branch is the prominent celiacomesenteric artery. The

celiacomesenteric is a major artery of the digestive tract. It will give rise to four branches

(although branching may vary between individuals). The first branch will enter into the liver and

is the hepatic artery. The next branch, which arises almost at the same point as the hepatic, is the

splenic artery that services the spleen. The third branch is the pancreaticoduodenal artery and is a

continuation of the celiacomesenteric. As its name indicates, it enters into the pancreas and

passes through the pancreas to the duodenum. The pancreaticoduodenal will also service the

pylorus. The fourth branch, which occurs only in some specimens, will be the first mesenteric

artery. Several additional mesenteric arteries will arise separately from the dorsal aorta. Each

will give rise to a number of smaller arteries that will vascularize the duodenum and ileum called

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the intestinal arteries. A series of paired arteries will originate from the dorsal aorta. Some will

service the testes or ovaries and are called generically the gonadal or genital arteries. More

specifically they can be named the testicular or ovarian arteries respectively. Another series of

paired arteries arising from the dorsal aorta in this region are the renal arteries. They are more

numerous than the genital arteries. These vessels will enter and vascularize the mesenephros.

Caudal to the last pair of renal arteries will arise the right and left iliac arteries. The iliac arteries

will exit the pelvis and enter into the thigh where they become the femoral arteries. A second

branch will arise from the iliac artery in the pelvis and will send branches into the cloaca and

bladder. This vessel is the hypogastric artery.

Necturus Visceral Blood Vessels 2

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Necturus Visceral Blood Vessels 3

Necturus Visceral Blood Vessels 4

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Necturus Pelvic Arteries

Veins will drain blood from capillary beds. As we saw in Squalus, in a triple-injected

Necturus specimen the veins will have two colors. Yellow vessels designate veins of the hepatic

portal system. Blue vessels designate systemic veins. Necturus will also have a renal portal

system component to the systemic division.

The hepatic portal system is a series of veins draining the capillary beds of the digestive

tract and delivering this nutrient-rich blood to the liver for processing. The hepatic portal vein is

located in a cleft along the dorsal aspect of the liver. It will enter the liver and break up into the

liver sinusoids. The hepatic portal vein drains the mesenteric, gastrosplenic, and the ventral

abdominal veins. The gastrosplenic vein drains the gastric vein and the splenic vein. It joins

with the mesenteric vein within the pancreas. The mesenteric vein is a singular vessel running

through the mesentery dorsal to the intestines. It will receive blood from a number of intestinal

veins that drain intestinal capillary beds. The ventral abdominal vein services both the hepatic

portal system and a portion of the systemic circulation called the renal portal system.

The renal portal system drains blood from the tail, pelvis, and hind limbs and delivers it

to the kidneys for the processing of metabolites. As in Squalus, the renal portal system of

Necturus includes a caudal vein that drains the tail. It will divide into the two renal portal veins.

The renal portal veins will run lateral to the mesenephros and give rise to numerous afferent

renal veins that will enter the kidneys. The right and left renal portal veins will continue to run

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Intestinal Veins Mesenteric V. Pancreaticoduodenal V. Gastrosplenic V.

Necturus Hepatic Portal System

160

along the lateral surface of the kidney until at the cranial aspect of the mesenephros where they

will give rise to the right and left posterior cardinal veins. The renal portal veins will also

receive small branches from the body wall called parietal veins. In addition, the iliac veins drain

into the renal portal veins. The iliac vein will drain the hind limb via the femoral vein. At the

junction of the femoral and the iliac veins will arise the ventral abdominal vein. The ventral

abdominal vein connects into the hepatic portal system. This vessel is typically lost when the

abdominal wall is opened.

Renal Portal V. Genital Veins Hepatic V. Hepatic Portal V.

Efferent & Afferent Renal Veins Posterior Vena Cava Intestinal V.

Necturus Some Renal Portal Veins

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Pulmonary V. Posterior Cardinal V. Dorsal Aorta Postcava Hepatic Portal V.

Parietal Arteries & Veins

Necturus Posterior Vena Cava and Some Other Veins

A prominent systemic vein of the posterior body is the posterior vena cava (a.k.a.;

postcava/post cava). It begins medial to the kidneys and runs through the pleuroperitoneal

cavity. At its starting point it will drain the efferent renal veins and the genital veins. As it

travels through the pleuroperitoneal cavity it enters into the liver. It travels cranially through the

liver, receiving blood from several hepatic veins along its length, and will eventually drain into

the hepatic sinus. The hepatic sinus drains into the common cardinal veins that will deliver

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blood to the sinus venosus. The common cardinal veins ultimately drain most of the systemic

veins. The sinus venosus delivers blood to the right atrium. Once the posterior vena cava enters

the liver you will have a difficult time seeing its other connections. The posterior cardinal veins,

which arose from the renal portal veins, will travel along the dorsal wall of the pleuroperitoneal

cavity immediately flanking the dorsal aorta. These vessels receive blood along their lengths

from a number of parietal veins that drain the dorsal body wall cranial to the mesenephros. The

posterior cardinal veins will deliver blood to the common cardinal veins. Based on the quality of

injection, you may be able to observe the subclavian vein. It will also drain into the common

cardinal vein. The subclavian vein receives blood from the brachial vein by way of the axillary

vein. These three vessels will be running parallel to the similarly named arteries. Another vein

located in the pleuroperitoneal cavity is the pulmonary vein. The right and left pulmonary veins

drain the right and left lungs respectively. The two pulmonary veins will anastomize to form the

pulmonary trunk. The pulmonary trunk will enter into the left atrium. The systemic veins

anterior to the pleuroperitoneal cavity are rarely injected and so will be difficult to observe at

best.

Part E3: The Circulatory System in Felis

The heart of Felis is located in the pericardial cavity of the thoracic cavity. It will be

surrounded by the pericardium. As noted before, be careful when removing the pericardium so as

to avoid losing the vagus nerve (CN.X). The vagus nerve will help to modulate the heartbeat.

Mammals have a “four chambered heart”. The four chambers are two atria and two ventricles.

Unlike most vertebrates, adult mammals lack a sinus venosus. Instead the blood vessels that

ancestrally drained into the sinus venosus will drain directly into the right atrium. These vessels

are the superior vena cava and inferior vena cava. The ancestral location of the sinus venosus in

mammals is marked by the location of the sinoatrial node. Externally the atria in mammals have

outpocketings called auricles. The auricles will be a darker brown color, which makes them easy

to distinguish from the ventricles. Internally the right and left atria are completely separated by

an interatrial septum. The right atrium receives deoxygenated blood from the superior and

inferior vena cavae. The left atrium receives oxygenated blood from the lungs by way of the

pulmonary veins. Externally the right and left ventricles can be easily observed. They will be a

paler shade of brown than will be the auricles. The two ventricles are externally divided by a

groove on the ventral wall of the heart called the anterior interventricular sulcus. An anterior

interventricular artery and vein will be located in this sulcus and are part of the coronary blood

vessels. Internally the ventricles are separated by a complete interventricular septum to prevent

the mixing of oxygenated and deoxygenated blood. The right ventricle will send deoxygenated

blood into pulmonary circulation by way of the pulmonary trunk. The left ventricle will send

oxygenated blood into systemic circulation by way of the aorta, the largest artery of the body.

The walls of the four chambers will vary in thickness based on the amount of cardiac muscle

present. The amount of cardiac muscle in a chamber correlates with function. As a result

ventricles, which pump blood further than do atria, are more muscular than are atria.

Anastomizing muscular ridges on the luminal surface of the ventricle called trabeculae carnae

reinforce the ventricular walls. Amniote hearts have valves designed to prevent the backflow

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Felis Arteries

1. R. Common Carotid 2. L. Common Carotid 3. Transverse Scapular 4. Thyrocervical

5. Internal Mammillary 6. L. Subclavian 7. Brachiocephalic 8. Vertebral

9. Costocervical 10. Ventral Thoracic 11. Long Thoracic 12. Thoracodorsal

13. R, Subclavian 14. Subscapular 15. Axillary 16. Brachial

17. Arch of Aorta 18. Pulmonary Trunk 19. Pulmonary Arteries 20. Thoracic Aorta

21. Abdominal Aorta 22. Celiac Trunk 23. Hepatic 24. (L.) Gastric

25. Splenic 26. Superior Mesenteric 27. Adrenolumbar 28. Renal

29. Posterior Pancreaticoduodenal 30. Mesenterics 31. Intestinals

32. R. Colic 33. Ileocolic 34. Middle Colic 35. L. Colic

36. Inferior Mesenteric 37. Genital 38. Adrenolumbar 39. External Iliac

40. Femoral 41. Popliteal 42. Saphenous 43. Internal Iliac

44. Caudal/Hypogastric/Median Sacral

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Felis Veins

1. Anterior Facial 2. Posterior Facial 3. Transverse Jugular 4. Internal Jugular

5. Inferior Thyroid 6. External Jugular 7. Transverse Scapular 8. Brachiocephalic

9. Subclavian 10. Subscapular 11. Ventral Thoracic 12. Long Thoracic

13. Thoracodorsal 14. Brachial 15. Axillary 16. Costovertebral

18. Sternal 18. Azygos 19. Superior Vena Cava 20. Inferior Vena Cava

21. Pulmonary 22. Adrenolumbar 23. Renal 24. Genital

25. Ilioliumbar 26. Common Iliac 27. External Iliac 28. Internal Iliac

29. Femoral 30. Popliteal 31. Greater Saphenous 32. Caudal

33. Posterior Pancreaticoduodenal 34. Superior Mesenteric 35. Mesenterics

36. Intestinals 37. Ileocolic 38. Inferior Mesenteric 39. Hepatic Portal

Note: Systemic veins are in blue and veins of the hepatic portal system are in yellow.

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of blood. Each valve consists of one or more flaps of fibrous connective tissue called cusps. The

atrioventicular (AV) valves prevent the backflow of blood from the ventricles into the atria. The

AV valves are anchored by connective tissue strands called cordae tendineae to bundles of

smooth muscle called papillary muscle. A second pair of valves, the semilunar valves prevent the

backflow of blood from the arteries (i.e.; aorta and pulmonary trunk) into the ventricles.

Left Ventricle Right Ventricle Right Auricle (of the R. Atrium)

Felis External Heart (L. Atrium is out of view)

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Left Atrium

Felis Internal Heart

As is true for all amniotes, the circulatory system of Felis consists of a pulmonary circuit

and a systematic circuit. The pulmonary circuit begins with the right ventricle which sends

deoxygenated blood to the lungs by way of the pulmonary trunk. The pulmonary trunk will

divide into the right and left pulmonary arteries to service the right and left lung respectively.

External respiration will occur in the lungs and the oxygenated blood will return to the heart

through the pulmonary veins. The pulmonary veins will empty into the left atrium completing

the pulmonary circuit. The systemic circuit begins with the left ventricle. The left ventricle

sends this oxygen-rich blood out to the body via the aorta. The aorta will give rise to a number of

arteries that serve to carry the blood to all of the tissues of the body. Internal respiration will

occur in these tissues. The deoxygenated blood will be recovered from these tissues by a series

of veins. The veins will ultimately drain into the superior and inferior vena cavae. These two

large veins drain into the right atrium completing the systemic circuit.

The arteries can be observed throughout the body. We will begin with the thoracic cavity.

The pulmonary trunk may be observed exiting the heart and passing under the arch of the aorta.

The pulmonary trunk will divide into a right and left pulmonary artery. These two vessels will

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Felis Upper Body Arteries1

further subdivide to send a vessel into each lobe of the lung. These pulmonary arteries can be

observed running between the heart and lungs. They will be blue instead of the typical red color

since they are carrying deoxygenated blood. The pulmonary arteries are the remnants of the sixth

aortic arch. The aorta of mammals is equivalent to the dorsal aorta of Squalus and Necturus. It

is a cane-shaped vessel beginning with an ascending aorta that extends a short way cranially. The

aorta then curves back and will run caudally throughout the thoracic and abdominopelvic

cavities. The curving portion is called the arch of the aorta and the caudally running portion is

generally called the descending aorta. Two major branches arise from the arch of the aorta. The

first is the brachiocephalic artery. The brachiocephalic artery will give rise to three primary

branches: right subclavian, right common carotid, and left common carotid. The two carotid

arteries will travel to the head and run medial to, and dorsolateral to, the trachea. Immediately

lateral to the common carotid arteries will be the right and left vagus nerves. A minor branch

will also arise from the brachiocephalic, the sternal artery. The sternal is a short vessel arising

half way along the ventral surface of the brachiocephalic. It will extend to the sternum. The

second branch coming off of the arch of the aorta is the left subclavian artery. (In humans three

major arteries branch off of the arch of the aorta: brachiocephalic, left common carotid, and left

subclavian.) Although they differ in length and point of origin, both the right and left

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Brachial Thoracodorsal Long Thoracic Ventral Thoracic Common Carotids Thyrocervical Subscapular

Axillary Brachiocephalic Aorta Pulmonary Trunk Subclavian Vertebral Costocervical

Felis Upper Body Arteries 2

subclavian will run to the forelimb and will show a similar branching pattern. The subclavian

will extend cranially through the thorax and will curve to the arm. The curving point is under the

clavicle in humans explaining the name for this artery. Prior to the curving point the subclavians

will give rise to three vessels. The first branch is the vertebral artery that will travel dorsally

towards the vertebrae. The second branch arises close to the vertebral and is called the

costocervical artery. The costocervical will travel a short distance dorsally and then branch into

the costal and cervical arteries. The third branch occurs near the curving point. It is the internal

mammary artery. This vessel travels ventrally to exit the rib cage and service the mammaries. It

was cut when the rib cage was opened. At the curve of the subclavian artery another vessel will

arise, the thyrocervical artery. The thyrocervical artery will extend a short way into the neck. At

its terminus the thyrocervical will give rise to several small vessels. One will extend over the

shoulder and is the transverse scapular artery. At the point that the thyrocervical diverges from

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the subclavian the subclavian enters the axilla and becomes the axillary artery. The axillary

artery will have three smaller arteries arise from it as it travels through the axilla. Typically all

three vessels will have been severed during your dissection and will appear as shortened nubs.

The first branching is the ventral thoracic artery (a.k.a.; anterior thoracic artery). This artery will

service the pectoralis major. The second artery to branch off of the axillary is the long thoracic

artery. The long thoracic artery will deliver blood to the pectoralis minor and xiphihumeralis.

The third artery to split from the axillary is the thoracodorsal artery. The thoracodorsal services

the latissimus dorsi and, due to its location, is the least likely of the three to be cut during your

dissection. At the terminus of the axillary artery one more artery will arise, the subscapular

artery. It enters into the subscapularis. The axillary at this point becomes the artery of the arm,

the brachial artery. The brachial artery will run along the humerus.

Common Carotids Transverse Scapular Thyrocervical Costocervical Vertebral Subclavian

Vagus N. Subscapular Brachial Axillary Thoracodorsal Long Thoracic Internal Mammary

Felis Upper Body Arteries 3

The descending aorta can be regionally divided into the thoracic aorta and the abdominal

aorta. The thoracic aorta will give rise to a number of small arteries that will run between the

ribs called intercostal arteries. The descending aorta becomes the abdominal aorta once it

penetrates the diaphragm. It will give rise to a number of visceral arteries and arteries of the

pelvis and hindlimb.

The first visceral branch to arise from the abdominal aorta is the celiac trunk. This is a

short, thick artery that will give rise to three other arteries. The first is the hepatic artery that will

enter the liver. The second is the left gastric artery that enters into the stomach along the greater

curvature. The third is the splenic artery which is actually the continuation of the celiac. It will

service the spleen. The second visceral branch is the superior mesenteric artery. This is large

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Felis Cranial Abdominal Arteries

artery that vascularizes the pancreas, small intestine, and much of the large intestine. It will give

rise to a number of branches: posterior pancreaticoduodenal, mesenterics, ileocolic, right colic,

and middle colic arteries. The first branch of the superior mesenteric is the posterior

pancreaticoduodenal artery (a.k.a.; inferior pancreaticoduodenal) that will run through the

duodenal lobe of the pancreas and enter the duodenum near the pyloric junction. A number of

arteries will arise caudal to the branching point for the posterior pancreaticoduodenal. These are

the mesenteric arteries. The mesenteric arteries travel through the mesentery and will further

divide into smaller vessels servicing the walls of the small intestine called intestinal arteries.

Caudal to the diverging point of the mesenterics will arise the ileocolic artery, then the right colic

artery, and finally the middle colic artery. The ileocolic will enter into the colon at the ileocolic

junction. The right colic enters into the ascending colon near the ileocolic junction. The middle

colic will run along the wall of the transverse and descending colon until it anastomizes with the

left colic artery. Caudal to the branching point of the superior mesenteric will arise the paired

adrenolumbar arteries. These vessels will service the adrenal gland and a portion of the lumbar

musculature. Along the length of the abdominal aorta a series of smaller paired arteries will arise

and enter into the lumbar musculature called lumbar arteries. Immediately caudal to the

origination point of the adrenolumbar will arise a second prominent pair of arteries, the renal

arteries, which service the kidneys. Caudal to this point a smaller pair of vessels will branch off

of the abdominal aorta, the gonadal arteries. The gonadal arteries will arise at the same point in

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Right Colic Ileocolic Middle Colic (cut) Superior Mesenteric Celiac Trunk Adrenolumbar

Felis Some Visceral Arteries 1

Felis Some Visceral Arteries 2

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Felis Abdominopelvic Vessels 1

males and females. In females they are shorter vessels called ovarian arteries that will

vascularize the ovary and send branches along the uterine cornua. In males these vessels are

named testicular/spermatic arteries and will descend with the testes into the scrotum during

development. As a result, testicular arteries are longer and will be a portion of the spermatic

cord along part of their length. The next branch to originate from the abdominal aorta is the

singular inferior mesenteric artery. The inferior mesenteric will enter the caudal one third of the

descending colon and will send out a branch called the left colic. The left colic artery will travel

along the wall of the descending colon until it anastomizes with the middle colic artery. At the

crest of the ilium a pair of vessels will arise from the abdominal aorta termed the iliolumbar

arteries. The abdominal aorta terminates at the lesser pelvic brim giving rise to the paired

external iliac, paired internal iliac, and singular hypogastric arteries. The external iliac arteries

will travel along the greater pelvic brim and exit the pelvis through the body wall. At this point

they give rise to a major artery, the femoral, and several smaller vessels. The femoral will travel

through the thigh along the femur until it branches into two arteries near the knee. One branch,

the popliteal artery, dives deep and travels to the posterior knee. The other branch is the

saphenous artery and will be a continuation of the femoral traveling along the medial shin. The

internal iliac artery will dive deep into the pelvis and give rise to a number of smaller branches.

In humans the external and internal iliacs arise from a common vessel named the common iliac

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artery. The hypogastric (a.k.a.; median sacral artery) will be located immediately ventral to the

sacrum and will travel into the tail as the caudal artery.

Felis Pelvic and Lower Abdominal Blood Vessels

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Saphenous A.(cut) Popliteal A. Femoral A. Internal Iliac A. External Iliac A.

Greater Saphenous V. Popliteal V. Femoral V.

Felis Thigh Blood Vessels

Veins will drain blood from capillary beds. As we saw in Squalus and Necturus, in a

triple-injected Felis specimen the veins will have two colors. Yellow vessels designate veins of

the hepatic portal system. Blue vessels designate systemic veins. Felis, unlike Squalus and

Necturus, lack a renal portal system component to the systemic division.

The tissues of the body cranial to the heart will heart will be drained by a series of

systematic veins that will ultimately drain into the superior vena cava. The superior vena cava

drains into the right atrium. This vessels is the right precava of other vertebrates. The superior

vena cava is fed by: right and left brachiocephalic, sternal, right and left costovertebral, and

azygous veins. The azygous vein is dorsal to the superior vena cava on the right. It will run

caudally (giving it a “cane-shape”) and drains the intercostal veins. The azygous is found in

amniotes and is the remains of the right posterior cardinal vein of other vertebrates. The azygous

also receives blood from the hemizygous. The hemizygous is a smaller vessel than the azygous

and is found medially on the left side of the posterior thoracic wall. It will drain the left

intercostal veins. The hemizygous is the remains of the left posterior cardinal vein of

nonamniotes. The right and left costovertebral veins typically drain into the superior vena cava

(although they may feed into one or both brachiocephalic veins in some specimens). These veins

are located near the costocervical and vertebral arteries. The costovertebral vein will divide into

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Felis Upper Body Veins

the costocervical and vertebral veins. Arising from the ventral surface of the superior vena at

approximately the halfway point of its length will be the sternal vein. The sternal vein will drain

the right and left internal mammary veins that will enter the ribcage from the surface of the

thorax. Depending on the amount of damage inflicted when you opened the ribcage, you may

see just the sternal or one or both of the two internal mammaries. The brachiocephalic veins are

a pair of large veins that drain the head and arms. They will receive blood from two primary

veins, the subclavian and jugular veins. The subclavian vein will vary in length but is typically

short (shorter than the subclavian artery that it runs with). It receives blood from the subscapular

and axillary veins. The subscapular vein drains smaller vessels of the subscapular region and can

be observed to enter the subscapularis. The axillary vein drains the ventral thoracic, long

thoracic, thoracodorsal, and brachial veins. The ventral thoracic, long thoracic, and

thoracodorsal veins will be similar to the similarly named arteries in terms of area serviced,

location, and having been cut during the dissection. The brachial vein will be located in the arm

and will run with the brachial artery. The jugular vein will branch into the external and internal

jugular veins. The internal jugular veins are rarely well injected. However, when they are, they

can be observed to run along the common carotids, in fact their tunica adventitiae will fuse

together. The external jugular vein is a prominent vessel and easy to observe. This vessel runs

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Superior Vena Cava Sternal Costovertebral Brachiocephalic Subclavian External Jugular

Axillary Thoracodorsal Long Thoracic Ventral Thoracic

Felis Some Thoracic Veins

lateral to the internal jugular and will be much larger. Partway along its length it will

communicate with the transverse scapular vein. The transverse scapular will extend dorsally over

the shoulder and will drain the cephalic vein of the dorsolateral arm. At it’s most cranial extent

the external jugular will receive blood from three vessels: posterior facial, anterior facial, and

transverse jugular veins.

Another set of upper body blood vessels is the right and left pulmonary veins. These

vessels and their tibutaries are not a portion of the systemic circuit but instead are part of the

pulmonary circuit. They will transport oxygen-rich blood from the lungs to the left atrium

(which is the end of the pulmonary circuit).. As a result, these vessels will not be blue but will

instead be red.

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Intercostal A. & V. Azygous V. Superior Vena Cava Sternal V. Vagus N.

Felis Features of the Posterior Thoracic Cavity

The systematic vessels of the body caudal to the heart will be drained by the inferior vena

cava (a.k.a.; posterior vena cava or postcava). The inferior vena cava runs from the pelvis,

through the diaphragm, into the thoracic cavity. In the abdominal cavity it will be located

immediately ventral to the vertebral column where it is situated along the dorsal aorta. The

inferior vena cava will deliver deoxygenated blood to the right atrium (which is the end of the

systematic circuit). The right and left popliteal and greater saphenous veins drain the legs. These

vessels run alongside the equivalent arteries. The popliteal drains the area posterior to the knee

and the greater saphenous drain the medial shin. Both vessels empty into the femoral vein. The

femoral vein will travel with the femoral artery and nerve. This is a nice example of a typical

anatomical pattern termed “NAVL” where the nerve, artery , vein, and lymph vessel will run

together. Often their outer tunics will join together to provide a greater combined strength. The

femoral vein will enter the body wall and it, along with some other veins, will deliver blood to

the external iliac vein. The external iliac vein will run along the greater brim of the pelvis. It will

drain into the common iliac vein. The common iliac vein will also receive blood from the

internal iliac vein which drains the inner pelvis. The left common iliac vein will typically also

receive blood from the caudal vein (a.k.a.; median sacral vein). This vessels is located

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Felis Pelvic and Lower Abdominal Blood Vessels

immediately ventral to the sacrum and will drain the tail. The right and left common iliacs will

join to form the caudal extent of the inferior vena cava. Normally this happens near the greater

pelvic brim but occasionally a specimen will appear to have the common iliacs joining near the

kidneys. In reality this is a case where the inferior vena cava has split and exists as a paired

structure until the two halves anastomize together near the renal veins. As the inferior vena cava

travels cranially through the abdominopelvic cavity it will receive blood from numerous small

lumbar veins. The first major vessels to deliver blood to the inferior vena cava are the iliolumbar

veins. These vessels, like the iliolumbar arteries, are located near the iliac crest. The next vein

to drain into the inferior vena cava is the right gonadal/genital vein. In females this would be the

ovarian and in males it would be the testicular/internal spermatic. The left gonadal vein delivers

blood into the left renal vein. This asymmetry is found in many species of placental mammal.

Notice the size of the ovarian veins when you study your specimen. The size can be correlated

with the female’s reproductive state at time of death. The next large veins to deliver blood into

the inferior vena cava are the right and left renal veins. Sometimes you will be able to observe

branches of the renal veins, called segmental veins, exiting at the hilus of the kidney. Cranial to

the renal veins will be the adrenolumbar veins. These vessels drain some of the lumbar

musculature and the adrenal glands. The adrenolumbar veins are the most cranial of the

abdominal systematic branches that you will be responsible for.

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Felis Hepatic Portal Veins 1

The hepatic portal system is a series of veins draining the capillary beds of the digestive

tract and delivering this nutrient-rich blood to the liver for processing. The hepatic portal vein is

a large, but short, vessel that delivers blood into the liver. It can be seen on the posterior right

side of the stomach near the lesser curvature of the stomach. The hepatic portal vein receives

blood from the superior mesenteric vein. The superior mesenteric vein is a large, long vessel that

receives blood from the pancreas, small intestine, and large intestine. It will run near, but not

quite parallel to, the superior mesenteric artery. One small vessel that drains into the cranial

portion of this vein is the inferior or posterior pancreaticoduodenal vein. This vein can be

observed traveling from the duodenum through the dorsal lobe of the pancreas. The caudal

portion of the superior mesenteric will fan out into a number of veins that will empty into it.

These vessels include the numerous intestinal veins that drain capillary beds of the small

intestine. As they travel towards the superior mesenteric they will join together to form several

mesenteric veins. The mesenteric veins will deliver blood into the superior mesenteric. The

superior mesenteric will also receive blood from the ileocolic and inferior mesenteric veins. The

ileocolic will arise from the ileocolic junction. The inferior mesenteric will drain the remainder

of the large intestine and will receive blood from the middle colic and right colic veins. The

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nutrient-rich blood will enter the sinusoids and will be processed by the liver. The resultant

blood, which will also be low in oxygen, will enter systemic circulation by draining into the

hepatic vein. The hepatic vein delivers the blood into the inferior vena cava immediately below

the diaphragm.

Superior Mesenteric V. Ileocolic A.& V. Right Colic A. Middle Colic A. Inferior Mesenteric. V. & A.

Felis Hepatic Portal Veins 1