SKULL

29.November.2011 TuesdayKaan Yücel M.D.,Ph.D.1

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The cranium (skull) is the skeleton of the head.

A series of bones form its two parts: Neurocranium Viscerocranium (Facial bones)

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The neurocranium is the bony case of the brain and its membranous coverings, the cranial meninges. It also contains proximal parts of the cranial nerves and the vasculature of the brain.

The neurocranium formed by 8 bones: 4 singular bones (Frontal, ethmoidal, sphenoidal, and occipital) 2 sets of bones bilateral pairs (Temporal and parietal)

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The neurocranium has a dome-like roof, calvaria (skullcap), and a floor or cranial base (basicranium).

The bones making the calvaria are primarily flat bones (frontal, parietal, and occipital).

The bones contributing to the cranial base are primarily irregular bones with substantial flat portions (sphenoidal and temporal).

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The bones contributing to the cranial base are primarily irregular bones with substantial flat portions (sphenoidal and temporal).

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The viscerocranium (facial skeleton) comprises the facial bones.

The viscerocranium forms the anterior part of the cranium and consists of the bones surrounding mouth (upper and lower jaws) nose/nasal cavity most of the orbits (eye sockets or orbital cavities).

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The viscerocranium consists of 15 irregular bones: 3 singular bones (mandible, ethmoid, and vomer) 6 bones bilateral pairs (maxillae; inferior nasal conchae; and zygomatic, palatine, nasal, and lacrimal bones).

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The maxillae and mandible house the teeth—that is, they provide the sockets and supporting bone for the maxillary and mandibular teeth.

The maxillae contribute the greatest part of the upper facial skeleton, forming the skeleton of the upper jaw.

The mandible forms the skeleton of the lower jaw.

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Several bones of the cranium (frontal, temporal, sphenoid, and ethmoid bones) are pneumatized bones, which contain air spaces (air cells or large sinuses), presumably to decrease their weight.

The total volume of the air spaces in these bones increases with age.

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Ossa Cranii Frontal Bone

Resembles a cockle-shell in form. Consists of two portions:

Squama, corresponding with the region of the foreheadOrbital portion, enters into the formation of the roofs of the orbital and nasal cavities.

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Articulates inferiorly with the nasal and zygomatic bones.

Also articulates with the lacrimal, ethmoid, and sphenoids.

Frontal Bone

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A horizontal portion of bone (orbital part) forms both the roof of the orbit and part of the floor of the anterior part of the cranial cavity.

The intersection of the frontal and the nasal bones is the nasion (L. nasus, nose); distinctly depressed area (bridge of nose).

Frontal Bone

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The supra-orbital margin of the frontal bone, the angular boundary between the squamous and the orbital parts, has a supra-orbital foramen or notch.

The internal surface of the squama frontalis of the frontal bone is concavePresents a ridge, frontal crest ; median bony extension of the frontal bone.

Frontal Bone

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Nasal process is the downward projection of the nasal part of the frontal bone which terminates as the nasal spine.

Frontal Bone

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Parietal Bones Form the roof of the cranium. Irregularly quadrilateral in form. The external surface is convex,, and marked near the center by

parietal eminence (tuber parietale). Crossing the middle of the bone in an arched direction are two

curved lines, superior and inferior temporal lines.

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Temporal BonesSituated at the sides and base of the skull.

Each consists of 5 parts, squama, petrous, mastoid, and tympanic parts, and t styloid process.

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The temporal fossa is bounded:Superiorly and posteriorly by the superior and inferior temporal lines, Anteriorly by the frontal and zygomatic bonesInferiorly by the zygomatic arch.

Temporal Bones

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The temporal bone contains, in its interior, the essential parts of the organ of hearing and the organ of equilibrium.

Temporal Bones

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Its inferior surface contains an oval depression which is called the mandibular fossa, articulates with the mandible.

Temporal Bones

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Sphenoid BoneSituated at the base of the skull in front of the temporals and basilar part of the occipital. Somewhat resembles a bat with its wings extended, and is divided into a median portion or body, two great and two small wings extending outward from the sides of the body, and two pterygoid processes which project from it below.

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Sphenoid Bone

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The sella turcica (L. Turkish saddle) is the saddle-like bony formation on the upper surface of the body of the sphenoid. Composed of 3 parts:• Tuberculum sellae (Horn of saddle)• Hypophysial fossa (Pituitary fossa)• Dorsum sellae (Back of saddle)

Sphenoid Bone

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On each side of the body of the sphenoid, a crescent of four foramina perforate the roots of the cerebral surfaces of the greater wings of the sphenoids: Superior orbital fissure Foramen rotundum (round foramen) Foramen ovale (oval foramen) Foramen spinosum (spinous foramen)

Sphenoid Bone

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ROLS

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Occipital Bone

Situated at the back and lower part of the cranium.

Pierced by a large oval aperture, foramen magnum, through which the cranial cavity communicates with the vertebral canal.

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The cranial base is formed posteriorly by the occipital bone, which articulates with the sphenoid bone anteriorly.

Occipital Bone

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The hypoglossal canal for the hypoglossal nerve (CN XII) is superior to the anterolateral margin of the foramen magnum.

Occipital Bone

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Ethmoid BoneSituated at the anterior part of the base of the cranium, between the two orbits, at the roof of the nose, and contributes to each of these cavities.

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Consists of 4 parts: A horizontal or cribriform plate, forming part of the base of the

cranium; A perpendicular plate, constituting part of the nasal septum;

Its numerous tiny foramina transmit the olfactory nerves (CN I).

Ethmoid Bone

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Cranial FossasAnterior cranial fossa Shallowest of the three cranial fossae.

Formed by the frontal bone anteriorly, the ethmoid bone in the middle, and the body and lesser wings of the sphenoid posteriorly.

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Middle cranial fossa Butterfly-shaped Has a central part composed of the sella turcica on the body of the

sphenoid.

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Posterior cranial fossa Largest and deepest of the three cranial fossae Formed mostly by the occipital bone, but the dorsum sellae of the

sphenoid marks its anterior boundary centrally and the petrous and mastoid parts of the temporal bones contribute its anterolateral “walls.”

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FACIAL BONES

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L. maxilla "upper jaw," diminutive of mala "jaw, cheekbone."

Largest bones of the face, excepting the mandibleForm, by their union, the whole of the upper jaw.

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Their alveolar processes include the tooth sockets (alveoli) and constitute the supporting bone for the maxillary teeth.

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The two maxillae are united at the intermaxillary suture in the median plane.

They have a broad connection with the zygomatic bones laterally.

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Each maxilla assists in forming the boundaries of 3 cavities:

Roof of the mouthFloor & lateral wall of the nose Floor of the orbit

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It also enters into the formation of two fossæ, the infratemporal and pterygopalatine, and two fissures, the inferior orbital and pterygomaxillary.

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Superiorly, each maxilla contributes to the inferior and medial rims of the orbit. Laterally, the zygomatic process of each maxilla articulates with the zygomatic bone.Medially, the frontal process of each maxilla articulates with the frontal bone.Inferiorly, the part of each maxilla, lateral to the opening of the nasal cavity, is the body of maxilla.

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The body of the maxilla is large and roughly pyramidal in shape. Its interior is hollowed out by the maxillary paranasal air sinus.

Upper (orbital) surface of the body occupies the floor of the orbit.

Anterior surface forms the curved external surface of the upper jaw.

Posterior (infratemporal) surface provides the anterior wall of the infratemporal fossa.

Medial (nasal) surface is a major structure component in the wall of the nasal cavity.

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Upper (orbital) surface of the body

Posterior (infratemporal) surface

Medial (nasal) surface

Anterior surface

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Maxillary tuberosity, located behind the last molar tooth.

More medially the lower part of the infratemporal surface articulates with the pyramidal process of the palatine bone.

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Maxillary tuberosity

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The four maxillary processes: (1) Zygomatic process (2) Frontal process (3) Palatine process (4) Alveolar process

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Above the incisor teeth, the anterior (oral) surface has shallow depression in the midline, termed the incisive fossa. It receives the lower openings of the two incisive canals which communicate above with the corresponding halves of the nasal cavity.

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Further laterally is the deeper canine fossa which is separated from the incisive fossa by the canine eminence produced by the root of the canine tooth.

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Above the canine fossa is the infraorbital foramen.

The anterior surface ends medially at the anterior nasal aperture.

At the inferior margin of this aperture the maxillae of the two sides form a median projection, the anterior nasal spine.

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The bony palate (the term hard palate is used to describe the bony palate plus its covering of mucous membrane; the bony palate thus forms the skeleton of the hard palate) provides the floor of the nasal cavity and the roof of the mouth.

Its anterior three-quarters are formed by the palatine process of the maxillae and its posterior one-quarter by the horizontal plates of the palatine bones.

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2 sutures cross the palate:Median suture between the elements of the right and left sides Transverse suture between the palatine processes of the maxillae and the horizontal plates of the palatines.

The four bony parts of the hard palate — the paired maxillary palatine processes (1) and the paired horizontal plates of the palatine bones (2) — form a cross-shaped suture (3), also known as the intermaxillary suture. This suture marks the juncture of each side of the hard palate; and the transverse suture (4), the junction of the maxillary and palatine bones.

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Medial to the last molar tooth on each side are the greater and lesser palatine foramina. Inferior openings of the greater palatine canal (pterygopalatine canal) which runs down from the pterygopalatine fossa. They transmit nerves and vessels of the same name.

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The posterior border of the palate has a median projection, termed the posterior nasal spine.

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In many skulls the bone either side of the median suture is heaped up to form a ridge. When pronunced this ridge is called the palatine torus.

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A- PZygomatic process of the maxillaZygomatic boneZygomatic process of the squamous part of the temporali

Zygomatic arch

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Pterygomaxillary fissure: Between the upper parts of the infratemporal surface of the maxilla and the anterior border of the pterygoid process.

Pterygopalatine fossa

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This leads medially from the infratemporal fossa into the pterygopalatine fossa, a small pyramidal space located just below the apex of the orbit.

Pterygopalatine fossa

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The fossa opens above through the posteromedial end of the inferior orbital fissure into the orbit.Three canals open on the posterior wall of the fossa: Foramen rotundum Pterygoid canal Palatovaginal canal

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The medial wall of the fossa is pierced by the sphenopalatine foramen. Between the body of the sphenoid & perpendicular plate of palatine. A communication between the ptergyopalatine fossa and nasal cavity.

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The principal contents of the pterygopalatine fossa:Maxillary nerve Pterygopalatine ganglionTerminal portion (third part) of the maxillary artery

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Mandible (Lower Jaw)L. mandibula "jaw," from L. mandere "to chew."

U-shaped bone with an alveolar process that supports the mandibular teeth.

Largest and strongest bone of the face, and it articulates with the skull at the temporomandibular joint.

Most inferior structure in the anterior view of the skull.

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Consists of a horizontal part, horseshoe-shaped, the body, and a vertical part, the ramus (a pair, hence pl. rami).

The body of the mandible meets the ramus on each side at the angle of the mandible.

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At birth the right and left halves of the mandible are united in the midline of the chin region by a fibrocartilaginous joint, symphysis menti (mandibular symphysis).

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External (buccal or labial) and Internal (lingual) surfaces.

Body of mandible is arbitrarily divided into two parts: Lower part = Base of mandible Upper part = Alveolar part of mandible

Body

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The upper part of the body of the mandible formed by alveolar process.Contains 16 sockets for the roots of the lower teeth and in life is covered by the mucoperiosteum of the lower gum.

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The base of mandible has a midline swelling mental protuberance on its anterior surface where the two sides of the mandible come together.

Just lateral to the mental protuberance are mental tubercles. Forms the prominence of the chin, A triangular bony elevation inferior to the symphysis menti Osseous union where the halves of the infantile mandible fuse.

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Running backwards and upwards from the mental tubercle is a faint ridge, the oblique line.

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Immediately above the oblique line, in the region of the premolar teeth, is the mental foramen. This transmits the mental branches of the inferior alveolar nerve and blood vessels - run in the mandibular canal within the body of the mandible.

The incisive canal is a continuation forward of the mandibular canal beyond the mental foramen and below the incisor teeth.Colours: blue = incisive canal, red = mental canal (the anterior opening of the mandibular canal) yellow = mandibular canal

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The internal surface of the body bears an oblique ridge, mylohyoid line, which begins a short distance below the last molar tooth as a prominent crest.

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Below the mylohyoid line is a concave area, submandibular fossa

Running forwards from the ramus into the submandibular fossa is the shallow mylohyoid groove.

Immediately above the line, in the region below the premolar teeth, is the shallow sublingual fossa.

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The inferior part of the internal surface below the incisor teeth bears two small elevations, superior and inferior mental spines.

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The inferior border of the body is marked digastric fossa for attachment of the anterior belly of the digastric muscle.

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Quadrilateral plate of bone. Vertically placed aHas an anterior coronoid process and a posterior condyloid process, or head; the two processes are separated by the mandibular notch (mandibular incisure).

Ramus

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A triangular plate of bone, projects upwards and forwards in front of the mandibular incisure.

On the anterior border of the ramus is the retromandibular fossa where the parotid gland is located.

Coronoid processs

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Expanded to form the head of the mandible.

In life the superior and posterior surfaces of the head are covered with fibrocartilage and articulate with the articular surgace of the squamos part of the temporal at the synovial temporomandibular joint.

The constricted part of the condylar process below the head neck of the mandible. Its anterior aspect has pterygoid fossa.

Condylar processs

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The constricted part of the condylar process below the head neck of the mandible.

Its anterior aspect has pterygoid fossa.

Condylar processs

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On the medial surface,approximately at the centre of the ramus of the mandible is the mandibular foramen; transmits the inferior alveolar nerve and blood vessels.

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In front of the mandibular foramen lingula. The foramen leads into the mandibular canal, which opens on the lateral surface of the body of the mandible at the mental foramen.

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Nasal bones are two small bones.Placed side by side at the middle and upper part of the face.

Laterally, each nasal bone articulates with the frontal process of each maxilla. With each other in the midline, with frontal bone superiorly.

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Small and quadrangular.Situated at the upper and lateral part of the face.Forms the prominence of the cheek, part of the lateral wall and floor of the orbit.Lie on the inferolateral sides of the orbits and rest on the maxillae.

ZYGOMATIC BONESMalar bone, Cheekbone

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Situated at the back part of the nasal cavity between the maxilla and the pterygoid process of the sphenoid.Contributes to the walls of 3 cavities: 1) Floor and lateral wall of the nasal cavity2) Roof of the mouth3) Floor of the orbit

PALATINE BONE

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The palatine bone resembles the letter L, and consists ofHorizontal plate of palatine bone Perpendicular plate of palatine bone 3 processesPyramidal process of palatine bone, Orbital process of palatine bone Sphenoidal process of palatine bone, which passes over the vertical part, and are separated by a deep notch;sphenopalatine notch.

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Formed by the palatal processes of the maxillae anteriorly and the horizontal plates of the palatine bones posteriorly.

Superior to the posterior edge of the palate are two large openings: the choanae (posterior nasal apertures), which are separated from each other by the vomer (L. plowshare), forms a major part of the bony nasal septum.

Hard palate (Bony palate)

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Inferior Nasal Concha extends horizontally along the lateral wall of the nasal cavity.

Lacrimal bone Smallest and most fragile bone of the faceSituated at the front part of the medial wall of the orbit.

Sutura is that form of articulation where the contiguous margins of the bones are united by a thin layer of fibrous tissue; it is met with only in the skull.Coronal sutureLambdoidal sutureSagittal suture

Important LandmarksGlabella: The most forward projecting point in the midline of the forehead at the level of the supra-orbital ridges and above the nasofrontal suture.Gnathion: The most anterior and lowest median point on the border of the mandible.

FontanellesThe bones of the calvaria of a newborn infant are separated by membranous intervals.

They include the anterior and posterior fontanelles and the paired sphenoidal and mastoid fontanelles.