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Head

Human Head• In anatomy, the head of an animal is the rostral part (from

anatomical position) that usually comprises the brain, eyes, ears, nose, and mouth (all of which aid in various sensory functions, such as sight, hearing, smell, and taste). Some very simple animals may not have a head, but many bilaterally symmetric forms do.

Bones of the headHuman skull

• The skull is divided into the cranium (all the skull bones except the mandible) and the mandible (or jawbone). One feature that distinguishes mammals and non-mammals is that there are also three ear bones (called ossicles):

• malleus (hammer) • incus (anvil) • stapes (stirrup)

Ossicles (Malleus,Incus,Stapes) Ossicles (also called auditory ossicles) are the three smallest bones in

the human body. They are contained within the middle ear space and serve to transmit sounds from the air to the fluid filled labyrinth (cochlea). The absence of the auditory ossicles would constitute a moderate to severe hearing loss.

Malleus Incus Stapes

Mandible

Jaw is either of the two opposable structures forming, or near the entrance to, the mouth.

Jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it.

In vertebrates, the lower jaw, dentary or mandible is the mobile component that articulates at its posterior processes, or rami (singular ramus), with the temporal bones of the skull on either side; the word jaw used in the singular typically refers to the lower jaw.

Mandible

A.) Bodya.) Symphysis mentib.) Mental protuberancec.) Mental foramend.) Mylohyoid line

B.) Ramusa.) Mandibular foramenb.) Mylohyoid groovec.) Mandibular canald.) Anglee.) Coronoid processf.) Condyloid processg.) Mandibular notch

Body of the Mandible

Mandible (from Latin mandibŭla, "jawbone") or inferior maxillary bone is, together with the maxilla, the largest and strongest bone of the face[citation needed]. It forms the lower jaw and holds the lower teeth in place.

Body of the mandible

Symphysis menti

Mental protuberance

Mental foramen

Mylohyoid line

Symphysis Menti

• The external surface of the mandible is marked in the median line by a faint ridge, indicating the symphysis menti or line of junction of the two pieces of which the bone is composed at an early period of life.

• This ridge divides below and encloses a triangular eminence, the mental protuberance, the base of which is depressed in the center but raised on either side to form the mental tubercle.

• It serves as the origin for the Geniohyoid and the Genioglossus.

Mental protuberance

Symphysis of the external surface of the mandible divides below and encloses a triangular eminence, the Mental protuberance, the base of which is depressed in the center but raised on either side to form the mental tubercle.

Mental foramen

Mental foramen is one of two holes ("foramina") located on the anterior surface of the mandible. It permits passage of the mental nerve and vessels. The mental foramen descends slightly in edentulous individuals

Mylohyoid line

• Extending upward and backward on either side from the lower part of the symphysis of the Mandible is the mylohyoid line, which is the origin of the mylohyoid muscle; the posterior part of this line, near the alveolar margin, gives attachment to a small part of the Constrictor pharyngis superior, and to the pterygomandibular raphé.

Ramus of the Mandible

• The ramus of the mandible (perpendicular portion) is quadrilateral in shape, and has two surfaces, four borders, and two processes.

Mandibular foramen

• The Mandibular foramen is an opening on the internal surface of the ramus (posterior and perpendicularly oriented part of the mandible) for divisions of the mandibular vessels and nerve to pass.

Mylohyoid groove• Behind this groove is a rough

surface, for the insertion of the Pterygoideus internus.

• The margin of the mandibular foramen is irregular; it presents in front a prominent ridge, surmounted by a sharp spine, the lingula mandibulæ, which gives attachment to the sphenomandibular ligament; at its lower and back part is a notch from which the mylohyoid groove runs obliquely downward and forward, and lodges the mylohyoid vessels and nerve.

Mandibular Canal

Mandibular canal runs obliquely downward and forward in the ramus, and then horizontally forward in the body, where it is placed under the alveoli and communicates with them by small openings.

• On arriving at the incisor teeth, it turns back to communicate with the mental foramen, giving off two small canals which run to the cavities containing the incisor teeth.

• Carries branches of inferior alveolar nerve and artery. Is continuous with the mental foramen (opents onto front of mandible) and mandibular foramen (on medial aspect of ramus).

Angle of the Mandible

At the junction of the lower border of the ramus of the mandible with the posterior border is the angle of the mandible, which may be either inverted or everted and is marked by rough, oblique ridges on each side, for the attachment of the Masseter laterally, and the Pterygoideus internus medially; the stylomandibular ligament is attached to the angle between these muscles.

Coronoid Process

Coronoid process is a thin, triangular eminence, which is flattened from side to side and varies in shape and size.

• Its anterior border is convex and is continuous below with the anterior border of the ramus.

• Its posterior border is concave and forms the anterior boundary of the mandibular notch.

• Its lateral surface is smooth, and affords insertion to the Temporalis and Masseter.• Its medial surface gives insertion to the Temporalis, and presents a ridge which

begins near the apex of the process and runs downward and forward to the inner side of the last molar tooth.

• Between this ridge and the anterior border is a grooved triangular area, the upper part of which gives attachment to the Temporalis, the lower part to some fibers of the Buccinator.

Condyloid Process

The condyle presents an articular surface for articulation with the articular disk of the temporomandibular joint; it is convex from before backward and from side to side, and extends farther on the posterior than on the anterior surface.

• Its long axis is directed medialward and slightly backward, and if prolonged to the middle line will meet that of the opposite condyle near the anterior margin of the foramen magnum.

• At the lateral extremity of the condyle is a small tubercle for the attachment of the temporomandibular ligament.

is thicker than the coronoid, and consists of two portions: the condyle, and the constricted portion which supports it, the neck.

Mandibular Notch

The upper border of the ramus of mandible is thin, and is surmounted by two processes, the coronoid process in front and the condyloid process behind, separated by a deep concavity, the mandibular notch.

Cranium • The cranium can be divided into a skull cap (or calvarium) and base.

The cranium consists of several bones which fuse together at junctions called sutures. Several sutures join to form a pterion.

• This process of bone fusion occurs in utero to protect the most important organ in the body, the brain. Although most fusing is complete before birth, there are large areas of fibrous tissue (called fontanelles) where fusion is incomplete until puberty.

• Facial and skull bones formed:• two maxillae (one on each side of the head) that cover the inferior and

medial to the eye socket (or orbit) • two zygomatic bones, inferior and lateral to the orbit • two temporal bones, covering an area where the ears are located • a single frontal bone, superior to the orbit • two parietal bones, posterior to the frontal bone and superior to the

temporal bone • an occipital bone at the back of the head • several more internal bones which are not easily seen which are

a sphenoid bone, ethmoid bone, two lacrimal bones, two nasal bones, two palatine bones, two nasal conchae, a vomer

Pterion• The point corresponding with the

posterior end of the sphenoparietal suture is named the pterion.

Location

• It is situated about 3 cm. behind, and a little above the level of the zygomatic process of the frontal bone.

• It marks the junction between four bones:

• the parietal bone • the temporal bone • the sphenoid bone • the frontal bone

Fontanels• In human anatomy, a fontanelle (or

fontanel) is one of two "soft spots" on a newborn human's skull. There are, however, two more fontanelles of interest, the mastoid fontanelle, and the sphenoidal fontanelle.

• Fontanelles are soft spots on a baby's head which, during birth, enable the soft bony plates of the skull to flex, allowing the head to pass through the birth canal. Fontanelles are usually completely hardened by a child's second birthday, and will eventually form the sutures of the neurocranium.

MaxillaI.) Body of maxilla II.) Maxillary sinus

A.) Surfaces of body 1.) Anterior

a.) Incisive fossab.) Canine fossac.) Infraorbital foramend.) Anterior nasal spine

2.) Infratemporala.) Alveolar canalsb.) Maxillary tuberosity

3.) Orbitala.) Infraorbital grooveb.) Infraorbital canal

4.) Nasala.) Pterygopalatine canal

Processes

1.) Zygomatic process2.) Frontal process

a.) Agger nasib.) Anterior lacrimal

crest3.) Alveolar process4.) Palatine process

a.) Incisive foramenb.) Incisive canalsc.) Foramina of

Scarpad.) Premaxilla

e.) Anterior nasal spine

MaxillaMaxilla

is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible, which is also a fusion of two halves at the mental symphysis.

Function• The alveolar process of the maxilla holds

the upper teeth, and is referred to as the maxillary arch. The maxilla attaches laterally to the zygomatic bones (cheek bones).

• The maxilla assists in forming the boundaries of three cavities:

• the roof of the mouth • the floor and lateral wall of the nasal

antrum • the floor of the orbit • The maxilla also enters into the formation

of two fossae: the infratemporal and pterygopalatine, and two fissures, the inferior orbital and pterygomaxillary.

Body of the MaxillaBody of the Maxilla

is somewhat pyramidal in shape, and contains a large cavity, the maxillary sinus (antrum of Highmore).

• It has four surfaces - an anterior, a posterior or infratemporal, a superior or orbital, and a medial or nasal.

Maxillary Sinus

Maxillary sinus (or Antrum of Highmore)

is the largest of the paranasal sinuses, and is pyramidal in shape.

Surfaces of body

1.) Anterior a.) Incisive fossab.) Canine fossac.) Infraorbital foramend.) Anterior nasal spine

2.) Infratemporala.) Alveolar canalsb.) Maxillary tuberosity

3.) Orbitala.) Infraorbital grooveb.) Infraorbital canal

4.) Nasala.) Pterygopalatine canal

Anterior surface of the body of the maxilla

Anterior surface is directed forward and lateral ward. It presents at its lower part a series of eminences corresponding to the positions of the roots of the teeth. Just above those of the incisor teeth is a depression, the incisive fossa, which gives origin to the Depressor alae nasi; to the alveolar border below the fossa is attached a slip of the Orbicularis oris; above and a little lateral to it, the Nasalis arises.

Incisive fossa

On the anterior surface of the maxilla, just above the eminences corresponding to the incisor teeth is a depression, the incisive fossa, which gives origin to the Depressor alæ nasi; to the alveolar border below the fossa is attached a slip of the Orbicularis oris; above and a little lateral to it, the Nasalis arises.

Canine fossa

Lateral to the incisive fossa is another depression, the canine fossa; it is larger and deeper than the incisive fossa, and is separated from it by a vertical ridge, the canine eminence, corresponding to the socket of the canine tooth; the canine fossa gives origin to the Caninus.

Infraorbital ForamenAbove the canine

fossa is the infraorbital foramen, the end of the infraorbital canal; it transmits the infraorbital artery, vein, and infraorbital nerve.

Anterior Nasal Spine• Medially, the anterior surface

of the maxilla is limited by a deep concavity, the nasal notch, the margin of which gives attachment to the Dilatator naris posterior and ends below in a pointed process, which with its fellow of the opposite side forms the anterior nasal spine.

Infratemporal surface of the body of the maxilla

Infratemporal surface is convex, directed backward and lateralward, and forms part of the infratemporal fossa.

• It is separated from the anterior surface by the zygomatic process and by a strong ridge, extending upward from the socket of the first molar tooth. It is pierced about its center by the apertures of the alveolar canals, which transmit the posterior superior alveolar vessels and nerves.

Alveolar canals

The infratemporal surface of the maxilla is pierced about its center by the apertures of the alveolar canals, which transmit the posterior superior alveolar vessels and nerves.

Maxillary Tuberosity• At the lower part of the

infratemporal surface of the maxilla is a rounded eminence, the maxillary tuberosity, especially prominent after the growth of the wisdom tooth; it is rough on its lateral side for articulation with the pyramidal process of the palatine bone and in some cases articulates with the lateral pterygoid plate of the sphenoid.

• It gives origin to a few fibers of the Pterygoideus internus.

Orbital surface of the body of the maxilla

Orbital surface

is smooth and triangular, and forms the greater part of the floor of the orbit.

Infraorbital Groove• Near the middle of the posterior

part of the orbital surface of the maxilla is the infraorbital groove (or sulcus), for the passage of the infraorbital vessels and nerve.

• The groove begins at the middle of the posterior border, where it is continuous with that near the upper edge of the infratemporal surface, and, passing forward, ends in a canal, which subdivides into two branches.

Infraorbital canal

• One of the canals of the orbital surface of the maxilla, the infraorbital canal, opens just below the margin of the orbit.

Nasal surface of the body of the maxilla

• The nasal surface presents a large, irregular opening leading into the maxillary sinus. At the upper border of this aperture are some broken air cells, which, in the articulated skull, are closed in by the ethmoid and lacrimal bones.

Greater Palatine Canal

Greater palatine canal (or pterygopalatine canal)

is a passage in the skull that transmits the greater palatine artery, vein, and nerve between the pterygopalatine fossa and the oral cavity.

MaxillaA.) Four processes

1.) The zygomatic process 2.) The frontal process

a.) Agger nasib.) Anterior lacrimal crest

3.) The alveolar process 4.) The palatine process

a.) Incisive foramenb.) Incisive canalsc.) Foramina of Scarpad.) Premaxillae.) Anterior nasal spine

Zygomatic Process

The zygomatic process of the maxilla (malar process) is a rough triangular eminence, situated at the angle of separation of the anterior, zygomatic, and orbital surfaces.

Frontal ProcessFrontal process of the maxilla (nasal

process) is a strong plate, which projects upward, medialward, and backward, by the side of the nose, forming part of its lateral boundary.

• Its lateral surface is smooth, continuous with the anterior surface of the body, and gives attachment to the Quadratus labii superioris, the Orbicularis oculi, and the medial palpebral ligament.

Agger nasi

• The agger nasi (from agger meaning "mound or heap") is a small ridge on the lateral side of the nasal cavity. It is located midway at the anterior edge of the middle nasal concha, directly above the atrium of the middle meatus. It is formed by a mucous membrane that is covering the ethmoidal crest of the maxilla.

• It is also called the nasoturbinal concha and the nasal ridge.

Anterior lacrimal crest

• The lateral margin of the lacrimal fossa is named the anterior lacrimal crest, and is continuous below with the orbital margin; at its junction with the orbital surface is a small tubercle, the lacrimal tubercle, which serves as a guide to the position of the lacrimal sac.

Alveolar Process

The alveolar process is the thickened ridge of bone that contains the tooth sockets on bones that bear teeth. It is also referred to as the alveolar bone. In humans, the tooth-bearing bones are the maxilla and the mandible.

Palatine Process

• The palatine process of the maxilla (palatal process), thick and strong, is horizontal and projects medialward from the nasal surface of the bone.

• It forms a considerable part of the floor of the nose and the roof of the mouth and is much thicker in front than behind.

Incisive Foramen

• When the two maxillæ are articulated, a funnel-shaped opening, the incisive foramen, is seen in the middle line, immediately behind the incisor teeth.

Incisive Canal

• In the opening of the incisive foramen, the orifices of two lateral canals are visible; they are named the incisive canals or foramina of Stenson.

Foramina of Scarpa

• In the maxilla, occasionally two additional canals are present in the middle line of the palatine process; they are termed the foramina of Scarpa, and when present transmit the nasopalatine nerves, the left

passing through the anterior, and the right through the posterior canal.

Premaxilla

• The premaxilla is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals.

Anterior Nasal Spine• Medially, the anterior surface

of the maxilla is limited by a deep concavity, the nasal notch, the margin of which gives attachment to the Dilatator naris posterior and ends below in a pointed process, which with its fellow of the opposite side forms the anterior nasal spine.

Palatine Bone

• The palatine bone is a bone in the palate (Latin palatum; unrelated to palatium 'palace', from which other senses of palatine derive).

Palatine Bone1.) Pterygopalatine fossa2.) Pterygoid fossa 3.) Horizontal plate

a.) Posterior nasal spine4.) Perpendicular plate

a.) Pterygopalatine canalb.) Sphenopalatine foramenc.) Pyramidal process

5.) Processesa.) Orbital b.) Sphenoidal

Pterygopalatine Fossa

• The pterygopalatine fossa is a fossa in the skull.

Pterygoid fossa

• The pterygoid fossa

is an anatomical term for the fossa formed by the divergence of the lateral pterygoid plate and the medial pterygoid plate of the sphenoid bone.

Horizontal plate of palatine bone

• The horizontal part of the palatine bone (horizontal plate) is quadrilateral, and has two surfaces and four borders.

Posterior nasal spine• Its medial end of the posterior

border of the horizontal plate of palatine bone is sharp and pointed, and, when united with that of the opposite bone, forms a projecting process, the posterior nasal spine for the attachment of the Musculus uvulæ.

Perpendicular plate of palatine bone

• The vertical part (perpendicular plate) of the palatine bone is thin, of an oblong form, and presents two surfaces and four borders.

Greater palatine canal

• The greater palatine canal (or pterygopalatine canal) is a passage in the skull that transmits the greater palatine artery, vein, and nerve between the pterygopalatine fossa and the oral cavity.

Sphenopalatine foramen

• The sphenopalatine foramen is a foramen in the skull that connects the nasal cavity with the pterygopalatine fossa.

Pyramidal process of palatine bone

• The pyramidal process of the palatine bone projects backward and lateralward from the junction of the horizontal and vertical parts, and is received into the angular interval between the lower extremities of the pterygoid plates.

Orbital process of palatine bone

• The orbital process of the palatine bone is placed on a higher level than the sphenoidal, and is directed upward and lateralward from the front of the vertical part, to which it is connected by a constricted neck. It presents five surfaces, which enclose an air cell. Of these surfaces, three are articular and two non-articular.

Sphenoidal process of palatine bone

• The vertical part (perpendicular plate) of the palatine bone is thin, of an oblong form, and presents two surfaces and four borders.

Zygomatic BoneZygomatic bone (malar

bone)

is a paired bone of the human skull. It articulates with the maxilla, the temporal bone, the sphenoid bone and the frontal bone. It forms part of the orbit and is commonly referred to as the cheekbone. It is situated at the upper and lateral part of the face: it forms the prominence of the cheek, part of the lateral wall and floor of the orbit, and parts of the temporal and infratemporal fossae. It presents a malar and a temporal surface; four processes, the frontosphenoidal, orbital, maxillary, and temporal; and four borders.

Zygomatic Bone

Orbital processZygomaticofacial foramen

Zygomaticotemporal foramenZygomaticoörbital foramina

Orbital Process of the Zygomatic bone

Orbital process of the zygomatic bone is a thick, strong plate, projecting backward and medialward from the orbital margin.

Zygomaticofacial foramen The malar surface of the

zygomatic bone is convex and perforated near its center by a small aperture, the zygomaticofacial foramen, for the passage of the zygomaticofacial nerve and vessels; below this foramen is a slight elevation, which gives origin to the Zygomaticus.

Zygomaticotemporal foramen

• Near the center of the temporal surface of the zygomatic bone is the zygomaticotemporal foramen for the transmission of the zygomaticotemporal nerve.

Zygomaticoörbital foraminaOn the orbital process of the

zygomatic bone are seen the orifices of two canals, the zygomaticoörbital foramina; one of these canals opens into the temporal fossa, the other on the malar surface of the bone; the former transmits the zygomaticotemporal, the latter the zygomaticofacial nerve.

Temporal BoneTemporal bones

are situated at the sides and base of the skull.

• The temporal bone supports that part of the face known as the temple.

Parts• Each consists of five parts:• Squama temporalis • Mastoid portion • Petrous portion• Tympanic part• Styloid process (temporal)

Squama Temporalis

Squama of the temporal bone

forms the anterior and upper part of the bone, and is scale-like, thin, and translucent.

Mastoid portion of the temporal bone

Mastoid portion of the temporal bone

forms the posterior part of the temporal bone.

Petrous portion of the temporal bone

Petrous portion of the temporal bone or pyramid

is pyramidal and is wedged in at the base of the skull between the sphenoid and occipital. Directed medialward, forward, and a little upward, it presents for examination a base, an apex, three surfaces, and three angles, and contains, in its interior, the essential parts of the organ of hearing.

Tympanic part of the temporal bone

Tympanic part of the temporal bone

is a curved plate of bone lying below the squama and in front of the mastoid process.

Temporal styloid processStyloid process

is pointed piece of bone that extends down from the human skull, just below the ear.

Frontal boneFrontal bone

is a bone in the human skull that resembles a cockle-shell in form, and consists of two portions:

• A vertical portion, the squama frontalis, corresponding with the region of the forehead.

• An orbital or horizontal portion, the pars orbitalis, which enters into the formation of the roofs of the orbital and nasal cavities.

Frontal boneI.) Squama frontalis

a.) Frontal suture

b.) Frontal eminence

c.) Superciliary arches

d.) Glabella

e.) Supraorbital foramen

f.) Zygomatic process

g.) Sagittal sulcus

h.) Frontal crest

i.) Foramen cecum

II.) Pars orbitalisa.) Ethmoidal notch

b.) Lacrimal fossa

c.) Trochlear fovea

d.) Posterior ethmoidal foramen

e.) Anterior ethmoidal foramen

f.) Frontal sinus

g.) Frontonasal duct

Squama frontalis• There are two surfaces of the squama of the frontal

bone: the external surface, and the internal surface.

Frontal suture

Frontal suture is a dense connective tissue structure that divides the two halves of the frontal bone of the skull in infants and children. It usually disappears by the age of six, with the two halves of the frontal bone being fused together. If it does not disappear it may be called a "metopic suture" or "sutura frontalis persistens." If the suture is not present at birth (craniosynostosis) it will cause a keel-shaped deformity of the skull called "trigonocephaly."

Frontal Eminence• On the frontal bone, on either side

of the frontal suture, about 3 cm. above the supraorbital margin, is a rounded elevation, the frontal eminence (tuber frontale).

• These eminences vary in size in different individuals, are occasionally unsymmetrical, and are especially prominent in young skulls; the surface of the bone above them is smooth, and covered by the galea aponeurotica.

Superciliary Arches• On the squama frontalis of the

frontal bone, below the frontal eminences, and separated from them by a shallow groove, are two arched elevations, the superciliary arches; these are prominent medially, and are joined to one another by a smooth elevation named the glabella. The superciliary arches are more prominent in men

GlabellaGlabella

is the space between the eyebrows and above the nose. It is slightly elevated, and joins the two superciliary ridges.

Supraorbital foramenSupraorbital foramen

is a bony elongated path located above the eye socket and under the forehead. The supraorbital foramen lies directly under the eyebrow.

The supraorbital foramen arches transversely below the superciliary arches and is the upper part of the margin of the orbit, thin and prominent in its lateral two-thirds, rounded in its medial third, and presenting, at the junction of these two portions, the supraorbital notch or foramen for the supraorbital nerve and vessels (supraorbital artery and supraorbital vein.)

Zygomatic process of frontal bone

• The supraorbital margin of the frontal bone ends laterally in the zygomatic process, which is strong and prominent, and articulates with the zygomatic bone.

Sagittal Sulcus• The internal surface of the

squama frontalis of the frontal bone is concave and presents in the upper part of the middle line a vertical groove, the sagittal sulcus, the edges of which unite below to form a ridge, the frontal crest; the sulcus lodges the superior sagittal sinus, while its margins and the crest afford attachment to the falx cerebri.

• It also is part of the parietal, and occipital bones.

Frontal Crest• The internal surface of the

squama frontalis of the frontal bone is concave and presents in the upper part of the middle line a vertical groove, the sagittal sulcus, the edges of which unite below to form a ridge, the frontal crest; the sulcus lodges the superior sagittal sinus, while its margins and the crest afford attachment to the falx cerebri.

Foramen cecum (frontal bone)

• The frontal crest of the frontal bone ends below in a small notch which is converted into a foramen, the foramen cecum, by articulation with the ethmoid.

• This foramen varies in size in different subjects, and is frequently impervious; when open, it transmits a vein from the nose to the superior sagittal sinus. This has clinical importance in that infections of the nose and nearby areas can be transmitted to the meninges and brain from what is known as the danger triangle of the face.

Pars Orbitalis• The orbital or horizontal part of the frontal bone

(pars orbitalis) consists of two thin triangular plates, the orbital plates, which form the vaults of the orbits, and are separated from one another by a median gap, the ethmoidal notch.

Ethmoidal notchEthmoidal notch

separates the two orbital plates; it is quadrilateral, and filled, in the articulated skull, by the cribriform plate of the ethmoid.

• The margins of the notch present several half-cells which, when united with corresponding half-cells on the upper surface of the ethmoid, complete the ethmoidal air cells.

Lacrimal fossaThe inferior surface of each

orbital plate of the frontal bone is smooth and concave, and presents, laterally, under cover of the zygomatic process, a shallow depression, the lacrimal fossa (or fossa for lacrimal gland), for the lacrimal gland.

Trochlear foveaNear the nasal part

of the interior surface of the frontal bone is a depression, the trochlear fovea, or occasionally a small trochlear spine, for the attachment of the cartilaginous pulley of the Obliquus oculi superior.

Posterior ethmoidal foramen• Lateral to either olfactory

groove are the internal openings of the anterior and posterior ethmoidal foramina (or canals).

Posterior ethmoidal foramen opens at the back part of this margin under cover of the projecting lamina of the sphenoid, and transmits the posterior ethmoidal vessels and nerve.

Anterior ethmoidal foramen• Lateral to either olfactory groove

are the internal openings of the anterior and posterior ethmoidal foramina (or canals).

Anterior ethmoidal foramen, situated about the middle of the lateral margin of the olfactory groove, transmits the anterior ethmoidal vessels and the nasociliary nerve; the nerve runs in a groove along the lateral edge of the cribriform plate to the slit-like opening above mentioned.

Frontal sinus

Frontal sinuses, situated behind the superciliary arches, are rarely symmetrical, and the septum between them frequently deviates to one or other side of the middle line.

• Their average measurements are as follows: height, 3 cm.; breadth, 2.5 cm.; depth from before backward, 2.5 cm.

Frontonasal duct

• The frontal air sinuses are lined by mucous membrane, and each communicates with the corresponding nasal cavity by means of a passage called the frontonasal duct.

Parietal boneParietal bones

are bones in the human skull and form, by their union, the sides and roof of the cranium. Each bone is irregularly quadrilateral in form, and has two surfaces, four borders, and four angles.

Outer

Inner

BordersSagittal border, the longest and thickest, is dentated and

articulates with its fellow of the opposite side, forming the sagittal suture.

Frontal border is deeply serrated, and bevelled at the expense of the outer surface above and of the inner below; it articulates with the frontal bone, forming half of the coronal suture. The point where the coronal suture intersects with the sagittal suture forms a T-shape and is called the bregma.

Occipital border, deeply denticulated, articulates with the occipital, forming half of the lambdoid suture. That point where the sagittal suture intersects the lambdoid suture is called the lambda, because of its resemblance to the Greek letter.

Squamous border is divided into three parts: of these: • the anterior is thin and pointed, bevelled at the

expense of the outer surface, and overlapped by the tip of the great wing of the sphenoid;

• the middle portion is arched, bevelled at the expense of the outer surface, and overlapped by the squama of the temporal;

• the posterior part is thick and serrated for articulation with the mastoid portion of the temporal.

Angles• Frontal angle is practically a right angle, and corresponds

with the point of meeting of the sagittal and coronal sutures; this point is named the bregma; in the fetal skull and for about a year and a half after birth this region is membranous, and is called the anterior fontanelle.

• Occipital angle is rounded and corresponds with the point of meeting of the sagittal and lambdoidal sutures—a point which is termed the lambda; in the fetus this part of the skull is membranous, and is called the posterior fontanelle.

• Mastoid angle is truncated; it articulates with the occipital bone and with the mastoid portion of the temporal, and presents on its inner surface a broad, shallow groove which lodges part of the transverse sinus. The point of meeting of this angle with the occipital and the mastoid part of the temporal is named the asterion.

• Sphenoidal angle, thin and acute, is received into the interval between the frontal bone and the great wing of the sphenoid. Its inner surface is marked by a deep groove, sometimes a canal, for the anterior divisions of the middle meningeal artery.

Occipital boneOccipital bone,

a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoid in shape and curved on itself. It is pierced by a large oval aperture, the foramen magnum, through which the cranial cavity communicates with the vertebral canal.

• The curved, expanded plate behind the foramen magnum is named the squama occipitalis.

• The thick, somewhat quadrilateral piece in front of the foramen is called the basilar part of occipital bone.

• On either side of the foramen are the lateral parts of occipital bone.

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