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Anatomy of the skull (1) Dr. Akram Jaffar Ph.D.

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Objectives <ul><li>Identify the features of the major bones forming the cranial cavity. </li></ul><ul><li>Describe the major sutures. </li></ul><ul><li>Describe the structure of the flat bones forming the skull and their blood supply. </li></ul><ul><li>Discuss ossification of the skull and the changes that occur during postnatal development. </li></ul><ul><li>Locate important bony surface landmarks. </li></ul>

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<ul><li>The skull consists of the cranium and the face . </li></ul><ul><li>The cranium encloses the brain, and face hangs down below it </li></ul>

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Features of the flat bones of the skull The flat bones of the skull consist of a sandwich of cancellous bone (diploe) (G., diploos = double) between two layers of compact bone so they are extremely strong. As the diploe contains a red bone marrow it is drained by large veins (the diploic veins), which open into the nearest venous sinus. There are no accompanying diploic arteries as the blood supply of the bones of the skull is derived from the meningeal arteries Diploic veins The emissary veins connect the veins of the scalp with the dural venous sinuses inside the skull and are obviously a possible route for the spread of infection. Emissary veins

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Sutures <ul><li>almost all the bones of the skull articulate with each other by fibrous joints called sutures at which in the adult there is no movement. </li></ul><ul><li>The edges of the joint may be serrated or straight or overlapping (squamous suture). </li></ul><ul><li>Many of the bones forming the sutures eventually become united by bone ( synostosis ). </li></ul>Synostosis of the coronal suture

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Primary craniosynostosis Premature closure of the sutures of the skull results in skull deformities. When premature closure of the coronal or the lambdoid suture occurs on one side only, the skull is twisted and asymmetrical. The type of deformed skull that forms depends on which sutures close prematurely. Premature closure of the sagittal suture, results in a long, narrow, and wedge-shaped skull.

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Overlap suture, neonatal moulding of labour <ul><li>This is provided by the softness of the bones and their loose connections at the sutures </li></ul><ul><li>Within few days after birth, the shape of the calvaria returns to normal </li></ul>Compression force

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Sutures nomenclature <ul><li>The names of many of the sutures indicate the bones between which the suture in question lies. </li></ul><ul><li>In other cases, however, the terms are not so obvious: one must know, for instance, where the lambdoid suture is </li></ul>Interparietal suture lambdoid suture

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Frankfurt plane <ul><li>In the anatomical position, the skull is oriented so that the inferior margins of the orbits and the superior margin of the external acoustic meatus are horizontal, this is called the Frankfurt plane </li></ul>

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The normas Five views of the exterior of the skull are used in anatomical descriptions, each is spoken of as a norma Norma verticalis Norma frontalis Norma lateralis Norma basalis Norma occipitalis

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Norma verticalis

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Norma verticalis <ul><li>The vault of the skull is also called the calvaria. </li></ul><ul><li>The bones of the calvaria and underlying lobes of the brain have similar names (viz. Frontal, parietal, occipital, and temporal). </li></ul>frontal parietal occipital temporal

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Frontal bone ossification <ul><li>The frontal bone becomes ossified from two centers </li></ul><ul><li>There are left and right frontal bones at birth but normally they fuse to form a single frontal bone. </li></ul>Newborn skull frontal frontal

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<ul><li>Occasionally the frontal bones remain separate and the sagittal suture will therefore continue foreword to the root of the nose (metopic suture ) . </li></ul><ul><li>The metopic suture is always present at birth but usually disappears by 6-7 years of age (G., metopon = forehead) </li></ul>Metopic suture Persistent metopic suture in a young adult The metopic suture may persist throughout life and be mistaken for a fracture

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Sagittal suture <ul><li>Posterior to the frontal bone are the parietal bones which, meet in the midline to form the sagittal suture (hence the sagittal plane of the body). </li></ul>

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<ul><li>The junction between the frontal and the two parietal bones is the coronal suture , hence the coronal plane </li></ul><ul><li>coronal = relating to a crown which fits over the coronal suture </li></ul>Coronal suture

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Bregma <ul><li>The intersection of the coronal and sagittal sutures is called the bregma (G., the forepart of the head) </li></ul><ul><li>The bregma is the site of the anterior fontanelle (the &quot;soft spots&quot; of the baby's head) (F., fountain). </li></ul>

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<ul><li>At birth, the bones are quite widely separated so that there is a diamond-shaped area, bounded by the two frontal and the two parietal bones, which remain unossified. </li></ul>Anterior fontanelle The shape resembles an arrow hence the name sagittal suture

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Parietal foramen Transmits a small emissary vein from the superior sagittal sinus. Pierces each parietal bone near the sagittal suture.

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The vertex <ul><li>Is the most superior part of the skull and is located near the center of the sagittal suture </li></ul>

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Lambdoid suture <ul><li>The two parietal bones and the occipital meet at an inverted Y-shaped suture, which is therefore called the lambdoid (resembling the Greek letter lambda [  ]). </li></ul>

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Frontal and parietal eminences <ul><li>From the superior aspect of the skull, the parietal and frontal eminences are seen as bulges on each side of the bones. </li></ul>

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Norma occipitalis

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Norma occipitalis <ul><li>Most of the occipital bone can be seen. </li></ul><ul><li>The lambda is where the lambdoid and sagittal sutures intersect. </li></ul><ul><li>The posterior pole of the skull which is the part that will hit the ground first when falling backwards is located below the lambda . </li></ul>

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Sutural bones Sutural bone accessory bones commonly located in the lamboid suture. Sutural bone at the pterion Sutural bone at the sagittal suture <ul><li>Sutural bones are sometimes seen along other borders of the parietal bone </li></ul>

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Posterior fontanelle <ul><li>In the newborn skull, sagittal and lambdoid sutures do not quite meet and there is a triangular posterior fontanelle. </li></ul><ul><li>This is much smaller than the anterior fontanelle and it closes earlier before the end of the first year </li></ul>

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External occipital protuberance <ul><li>A projection located below the lambda </li></ul><ul><li>Can be felt by running a finger up to the midline groove at the back of the neck. </li></ul>

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Nuchal lines <ul><li>Stretching laterally from the external occipital protuberance are the superior nuchal lines and, below them the inferior nuchal lines </li></ul>

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Inferior nuchal lines <ul><li>The surface landmark for the attachment of the tentorium cerebelli, which straddles the transverse venous sinus). </li></ul>Tentorium cerebelli Transverse venous sinus Tentorium cerebelli Transverse venous sinus

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Superior nuchal lines <ul><li>The superior nuchal line is the superior limit of the neck. </li></ul><ul><li>The area below the superior nuchal lines is rough for the attachment of the extensor muscles of the neck. </li></ul><ul><li>The bone below the superior nuchal lines covers the cerebellar hemispheres </li></ul><ul><li>It provides attachment for sternocleidomastoid and trapezius musles. </li></ul><ul><li>Above the superior nuchal line is the highest nuchal line , which gives origin to occipitofrontalis muscle </li></ul>cerebellum

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The inion <ul><li>Is the summit of the external occipital protuberance </li></ul><ul><li>The inion lies opposite the interval between the occipital poles of the cerebrum. </li></ul><ul><li>It marks the termination of the straight and superior sagiittal sinuses and the commencement of the transverse sinus. </li></ul>Straight sinus Superior sagittal sinus

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Mastoid emissary foramen The mastoid foramen is near or in the occipitomastoid suture. The mastoid foramen transmits an emissary vein from the sigmoid sinus

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Norma lateralis

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Norma lateralis <ul><li>The squamous (flat) part of the temporal bone contributes to the sidewall of the cranium in the region popularly known as the temple </li></ul><ul><li>The name of the bone, from tempus = time, is supposed to be derived from the fact that this is the region where time first grays the hair. A good story but perhaps the German Schlafenbein, &quot;sleeping bone&quot;, is more descriptive. </li></ul>

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Asterion <ul><li>The meeting place of the temporo-parietal and lambdoid sutures is called the asterion </li></ul>

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Parts of the temporal bone <ul><li>Developmentally, the temporal bone is composed of four parts, the squamous, petrous, tympanic plate, and styliod process. </li></ul><ul><li>The mastoid process develops as a down growth from the petrous part, so the whole is often called petromastoid. </li></ul>squamous styloid petruos petruos Tympanic plate mastoid

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Tympanic plate <ul><li>The tympanic part of the temporal bone forms the floor and anterior and posterior walls of the external auditory meatus which is located in front of the mastoid process </li></ul><ul><li>The tympanic part in the fetus is in the form of a ring </li></ul>External auditory meatus

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Squamous temporal <ul><li>The squamous temporal forms the socket for the head of the mandible. </li></ul><ul><li>It also develops a forwardly projecting zygomatic process. </li></ul>Zygomatic process

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Zygomatic arch <ul><li>The zygomatic process of the temporal bone joins a similar process from the zygomatic bone to form with the zygomatic process of the maxilla, the zygomatic arch </li></ul><ul><li>(G., zygon = yoke; yoke = A crossbar with two U-shaped pieces that encircle the necks of a pair of oxen or other draft animals (A team of animals used to pull loads) working together. </li></ul><ul><li>The term zygoma is synonymous with the zygomatic process of the temporal bone only and does not include the whole arch. </li></ul>Zygomatic bone Zygomatic process (zygoma) Zygomatic process of maxilla Zygomatic arch

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Zygomatic arch <ul><li>The superficial temporal pulse may be felt at a point on the posterior root of the zygoma immediately anterior to the attachment of the auricle. </li></ul>

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Zygomatico-facial foramen <ul><li>The zygomatic arch is perforated by the zygomatico-facial foramen. </li></ul><ul><li>The zygomatico-facial foramen transmits an artery and a nerve of the same name. </li></ul>

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Pterion <ul><li>The greater wing of the sphenoid (sphenoid = wedge-shaped) forms an H-shaped suture with the frontal, parietal, and temporal bones. This region is called the pterion (G., ptereux = wing). </li></ul><ul><li>The pterion is situated 4 cm above the midpoint of the zygomatic arch, about 3cm posterior to the zygomatic process of the frontal bone. It is the site for surgical exploration of the middle meningeal artery. </li></ul>Middle meningeal artery

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Middle meningeal artery <ul><li>A branch of the maxillary artery. </li></ul><ul><li>Enter the cranial cavity through the foramen spinosum. </li></ul>Remember that this artery supplies the bone as well as the meninges.

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Middle meningeal artery <ul><li>Runs in an anterolateral groove on the squamous part of the temporal bone, dividing into frontal and parietal branches. </li></ul><ul><li>The frontal (anterior) branch, the larger, crosses the greater wing of the sphenoid, reaches a groove or canal. </li></ul>

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Middle meningeal artery <ul><li>The parietal (posterior) branch curves back on the squamous temporal bone, reaching the lower border of the parietal. </li></ul>If you put the pencil behind your ear you'll have a pretty good idea of the course of the posterior branch.

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Extradural haematoma <ul><li>Extradural haematomas are commonly due to bleeding from the middle meningeal artery </li></ul>The bone is relatively thin at the pterion and an extradural haematoma may follow a direct hit. <ul><li>Skull fracture with frontal collection of extradural haematoma </li></ul>

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Groove for the middle temporal artery The middle temporal artery , a branch of the superficial temporal artery, pierces the fascia and runs up vertically deep to temporalis. The middle temporal artery produces a vertical groove on the squamous part of the temporal bone

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Radiographic point This is a convenient place to mention that the auricle of the ear can be seen as a semicircular shadow on the lateral skull x-ray. 6 months

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Norma frontalis

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Norma frontalis (The skeleton of the face) <ul><li>There are a number of foramina of the face but most of them are very small. </li></ul><ul><li>Three of them are worthy of mention here. These are the supraorbital, infraorbital, and mental foramina and they lie on a vertical line. </li></ul>

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Norma frontalis (The skeleton of the face) <ul><li>The supraorbital, infraorbital, and mental foramina transmit the three major cutaneous nerves of the face. </li></ul>

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Norma frontalis (The skeleton of the face) <ul><li>The nerves have the same names as the foramina and each is a branch of a separate division of the trigeminal nerve, respectively the ophthalmic, maxillary, and mandibular divisions. </li></ul>

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Supraorbital foramen Supraorbital foramen and notch The supratrochlear foramen, usually a notch medial to the supraorbital foramen

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Infraorbital foramen Double foramen Transmits a nerve and vessels of the same name

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Mental foramen The mental foramen is in line with the longitudinal axis of the 2 nd premolar tooth Transmits a nerve and vessels of the same name

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<ul><li>The disproportion between the cranial vault and facial skeleton; the vault is very large in proportion to the face </li></ul>Features of the infant skull

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<ul><li>The fontanelles. </li></ul><ul><li>Metopic suture. </li></ul><ul><li>Absent mastoid process. </li></ul><ul><li>Stylomastoid foramen is near the lateral surface of the skull making the issuing facial nerve vulnerable </li></ul><ul><li>The tympanic part is a C-shaped ring. </li></ul><ul><li>The tympanic membrane faces downwards in the newborn but more laterally in the adult. </li></ul><ul><li>Shallow mandibular fossa. </li></ul><ul><li>Small maxilla and narrow maxillary sinus. </li></ul><ul><li>The mandible is in two halves that unite in the first year. </li></ul><ul><li>The mental foramen lies near the lower border of the mandible. </li></ul><ul><li>Angle of the mandible is is obtuse and the coronoid process lies at a higher level than the condyle </li></ul>Features of the infant skull

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Norma basalis

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Norma basalis (the base of the skull) <ul><li>The occipital, temporal, and sphenoid make the base of the cranium behind the face. </li></ul><ul><li>Many foramina are recognized </li></ul>Occipital bone Temporal bone Sphenoid bone Foramen ovale Foramen spinosum Foramen lacerum Carotid canal Jugular foramen Foramen magnum <ul><li>Near the foramen spinosum is the spine of the sphenoid </li></ul>Spine of The sphenoid <ul><li>The jugular foramen seen from below takes the form of a deep hollow which is occupied in life by the jugular bulb, an expansion of the internal jugular vein. </li></ul>

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Norma basalis (the base of the skull) <ul><li>Just lateral to the jugular foramen is the styloid process (L., stylus = pencil) </li></ul><ul><li>Postero-lateral to the styloid process is the mastoid process which can be felt deep to the lobe of the ear. </li></ul><ul><li>Between the styloid and mastoid processes is the stylomastoid foramen for the facial nerve. </li></ul><ul><li>The deep surface of the mastoid process is channeled into the digastric notch for the origin of the posterior belly of the digastric muscle. </li></ul><ul><li>Medial to the digastric notch is a groove for the occipital artery . </li></ul>Jugular foramen Styloid process Mastoid process Stylomastoid foramen

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Norma basalis (the base of the skull) <ul><li>In front of the jugular foramen, and therefore in the petrous temporal bone, is the carotid canal just in front of the internal jugular vein. </li></ul><ul><li>The carotid canal runs forwards and medially in the temporal bone and opens into the posterior wall of the foramen lacerum . </li></ul>Carotid canal Foramen lacerum

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Norma basalis (the base of the skull) ovale spinosum carotid jugular Stylomastoid lacerum The foramen ovale lies in front of spinosum; both in the greater wing of the sphenoid

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Course of the internal carotid artery <ul><li>It ascends in the neck and enters the carotid canal. It has a tortuous intracaranial course. </li></ul><ul><li>The tortuous portion known to radiologists as the carotid siphon . </li></ul>

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Norma basalis (the base of the skull) <ul><li>The spine of the sphenoid lies immediately medial to the mandibular (glenoid) fossa . This is part of the temporal bone so that jaw joint is known officially as the temporomandibular joint (or TMJ). </li></ul><ul><li>In front of the mandibular fossa is the convexity of the eminentia articularis . In front of this is the infratemporal surface formed by the squamous temporal and the greater wing of the sphenoid </li></ul>Spine of the sphenoid Glenoid fossa Eminentia articularis Infratemporal fossa

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Norma basalis (the base of the skull) <ul><li>Foramen ovale lies at the base of the downwardly projecting plate of bone, the lateral pterygoid plate . </li></ul><ul><li>At the tip of the medial plate is a little hook, the pterygoid hamulus . </li></ul><ul><li>The medial pterygoid plate is located more medially. The pterygoid plates are part of the sphenoid. </li></ul>Lateral Pterygoid plate Medial Pterygoid plate Pterygoid hamulus

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Norma basalis (the base of the skull) <ul><li>At the upper part of the medial pterygoid plate is the pterygoid tubercle which projects back towards foramen lacerum beyond the opening of the pterygoid canal ; the latter communicates with the pterygopalatine fossa. </li></ul><ul><li>Lateral to the pterygoid tubercle is the scaphoid fossa . </li></ul>Lateral Pterygoid plate Medial Pterygoid plate Pterygoid tubercle Pterygoid canal Foramen lacerum Scaphoid fossa

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Norma basalis (the base of the skull) <ul><li>The spine of the sphenoid overlies the opening in the petrous bone of the bony part of the Eustachean tube . </li></ul><ul><li>The cartilagenous part of the tube lies in the oblique slit between the greater wing of the sphenoid and the apex of the petrous temporal bone. </li></ul>Opening of the Bony part of the Eustachean tube

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Norma basalis (the base of the skull) <ul><li>The area behind foramen magnum shows the inferior nuchal line lying concentric with and halfway between foramen magnum and the superior nuchal line. </li></ul><ul><li>A rather vague line radiating back and out from the foramen magnum bisects each half; thus four areas are demarcated on each side of the external occipital protuberance these are for the attachment of the muscles of the suboccipital region . </li></ul><ul><li>In the midline between the external occipital protuberance and foramen magnum is the external occipital crest . </li></ul>Foramen magnum External Occipital protuberance 1 2 3 4

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Norma basalis (the base of the skull) <ul><li>Foramen magnum is oval with its long diameter being anteroposterior, its transverse diameter is that of the back of the nose between the medial pterygoid plates. </li></ul><ul><li>The occipital condyles lie at the lateral part of the front half of the foramen magnum. </li></ul><ul><li>The convex surfaces of the occipital condyles make a ball and socket joint with the atlas. The ball is oval-shaped like a ball lying on its side, and thus permits nodding and some abduction but no rotation (rotation is permitted at the pivot atlanto-axial joint ). </li></ul>Occipital condyle <ul><li>Deep to the occipital condyle, the bone is perforated by the hypoglossal canal . </li></ul>

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Norma basalis (the base of the skull) <ul><li>Behind the occipital condyle, there is a shallow fossa often perforated ( posterior condylar canal ) for a vein from the sigmoid sinus to the suboccipital venous plexus. </li></ul><ul><li>In front of foramen magnum is the basi-occiput which fuses at 25 years of age with the basi-sphenoid . </li></ul>Basi-occiput <ul><li>At the basiocciput, the pharyngeal tubercle is located and the bone forms the roof of the nasopharynx </li></ul>Pharyngeal tubercle

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Norma basalis (the base of the skull) <ul><li>Further forwards is the posterior opening of the nasal cavity in which lies the single midline vomer . </li></ul><ul><li>The medial pterygoid plate through its vaginal process articulates with the vomer at the vomerovaginal suture where a canal is present but transmits nothing. </li></ul>vomer <ul><li>The vomer is attached by a fibrous joint to the under surface of the body of the sphenoid. </li></ul>

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Norma basalis (the base of the skull) <ul><li>The hard palate is formed partly by the horizontal palatine process of the maxilla and posteriorly by the horizontal plate of the palatine bone . </li></ul>maxilla Palatine bone Alveolar process <ul><li>The hard palate is arched more by the downward projecting alveolar processes of the maxillae. </li></ul>Horizontal paltine Process of the maxilla maxilla Alveolar process Incisive foramen <ul><li>The incisive foramen is located anteriorly. </li></ul>Incisive foramen

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Norma basalis (the base of the skull) <ul><li>Posteriorly on each side of the hard palate, the greater palatine foramina lie in front of the crest of the palatine bone. Behind the crest are 2-3 lesser palatine foramina </li></ul><ul><li>Further behind is the tubercle of the palatine bone which, projects behind the tuberosity of the maxilla </li></ul>Crest of the Palatine bone Greater Palatine foramen Lesser Palatine foramen Greater Palatine foramen Tubercle of the Palatine bone Tuberosity of The maxilla <ul><li>In the posterior midline of the hard palate is the posterior nasal spine . </li></ul>Posterior Nasal spine