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CRANIUM OVERVIEW CRANIUM o Two parts Neurocranium—bony case of the brain and its membranous coverings Contains proximal parts of the cranial nerves and brain vasculature Formed by a series of 8 bones 1. Frontal, ethmoidal, sphenoidal, and occipital 1. Ethmoidal is actually a large part of viscerocranium 2. Temporal and parietal that come in pairs Calvaria is the roof Cranial base is the floor Bones united by sutures 1. Sphenoid and occipital are actually united by hyaline cartilage in childhood Viscerocranium—facial skeleton Develop from pharyngeal arches 15 irregular bones here 1. Mandible, ethmoid, vomer (3 in the midline) 2. Maxillae, inferior nasal conchae, zygomatic, palatine, nasal, and lacrimal bones (occur in pairs) PNEUMATIZED BONES Contain spaces for air—sinuses Frontal, temporal, sphenoid, and ethmoid bones o Facial aspect In some adults, metopic suture in the middle of the glabella occurs Intersection of frontal and nasal bones is the nasion Used as a landmark to document abnormalities Supraorbital margin of frontal bone has a supraorbital foramen for passage of the supraorbital nerve and vessels Just superior to subraorbital margin is superciliary arch—extends laterally on each side from the glabella Zygomatic bones from prominences of cheeks Zygomaticofacial foramen pierces the lateral aspect of the bone Piriform aperture—anterior nasal opening in the cranium Bony nasal septum inside Nasal conchae are curved bony plates on either side Maxillae form the upper jaw—alveolar processes form tooth sockets Two maxillae are united at the intermaxillary suture Infraorbital foramen inferior to eachorbit for passage of the infraorbital nerve and vessels Mandible Supports mandibular teeth Has a body and a ramus (vertical part) Mental foramina are inferior to second premolar teeth for mental nerves and vessels Mental protuberance forms the prominence of the chin 1. Inferior to mandibular symphysis—osseous union between the two halves of the mandible o LATERAL ASPECT OF CRANIUM Main features are temporal fossa, external acoustic opening, mastoid process of temporal bone—neurocranial part Infratemporal fossa, zygomatic arch, lateral aspects of maxilla and mandible— viscerocranial part Temporal fossa is bounded by superior and inferior temporal lines superiorly Zygomatic arch is formed by union of temporal process of the zygomatic bone and the zygomatic process of the temporal bone Remember pterion Union of frontal, parietal, sphenoid, and temporal bones External acoustic opening is the entrance to external acoustic meatus (canal) which leads to tympanic membrane Mastoid process of temporal bone Styloid process is anteromedial to mastoid process Slender and needle like Is part of temporal bone Infratemporal fossa is irregular space inferior and deep to zygomatic arch OCCIPITAL ASPECT OF CRANIUM Composed of occiput, parts of parietal bones, and mastoid parts of temporal bones External occipital protuberance/inion External occipital crest descends from protuberance towards foramen magnum Has superior and inferior nuchal lines Lambda indicates the junction of sagittal and lambdoid sutures May also have sutural bones (accessory bones) SUPERIOR ASPECT OF CRANIUM Broadens posteriorly at parietal eminences Frontal eminences may also be visible here Coronal suture separates frontal and parietal bones Sagittal suture separates parietal bones Lambdoid suture separates parietal and temporal bones from the occipital bone Bregma is where intersection or sagittal and coronal sutures is Vertex is most superior part of calvaria—near midpoint of sagittal sutures Parietal foramen is located posteriorly in the parietal bone near sagittal suture Emissary foramina transmit emissary veins connecting scalp veins to venous sinuses of the dura mater EXTERNAL SURFACE OF CRANIAL BASE Features alveolar arch of maxillae (free border of alveolar processes surrounding and supporting maxillary teeth), palatine processes of maxillae, palatine, sphenoid, vomer, temporal, and occipital bones Hard palate is formed by palatal processes of maxillae anteriorly and horizontal plates of palatine bones posteriorly Posterior nasal spine—free posterior border of hard palate projects posteriorly in the median plane as this Incisive fossa is here Right and left nasopalatine nerves pass from nose through a variable number of incisive canals and foramina (may be bilateral or merged into a single formation) Posterolaterally, greater and lesser palatine foramina occur Superior to the posterior edge of the palate are two large openings: choanae (posterior nasal apertures), which are separated from each other by the vomer Sphenoid—irregular unpaired bone with 3 processes Greater wings, lesser wings, pterygoid processes Greater and lesser wings spread laterally from lateral aspects of the body of the bone Greater wings have orbital, temporal, and infratemporal surfaces apparent in facial, lateral, and inferior views of the exterior of cranium Pterygoid processes consist of lateral and medial pterygoid plates—extend inferiorly on each side of the sphenoid from the junction of the body and greater wings Groove for cartilaginous part of the pharyngotympanic (auditory) tube lies medial to spine of sphenoid Inferior to greater wing of sphenoid and petrous part of temporal bone Depressions in squamous part of temporal bone are called mandibular fossae Accommodate mandibular condyles when mouth is closed o o o Foramen magnum is seen—structures passing through it are spinal cord, meninges, vertebral arteries, anterior and posterior spinal arteries, spinal accessory nerve (CN XI) Occipital condyles allow cranium to articulate with vertebral column Jugular foramen—opening between the occipital bone and petrous part of the temporal bone Internal jugular vein, CN IX—CNXI emerge from the cranium from here Entrance to carotid canal for internal carotid artery is just anterior to the jugular foramen Mastoid processes provide for muscle attachments Stylomastoid foramen, transmitting facial nerve (CNVII) and stylomastoid artery, lies posterior to base of styloid process INTERNAL SURFACE OF CRANIAL BASE Three large depressions—anterior, middle, and posterior cranial fossae Form the floor of the cranial cavity ANTERIOR CRANIAL FOSSA Inferior and anterior parts of frontal lobes occupy Formed by frontal bone anteriorly, ethmoid bone in the middle, and the body and lesser wings of sphenoid posteriorly Frontal crest – median bony extension of the frontal bone 1. Foramen cecum of the frontal bone, which gives passage to vessels during fetal development but is insignificant postnatally Crista galli – thick, median ridge of bone posterior to foramen cecum—projects superiorly from the ethmoid bone 1. On each side of this is the cribriform plate of ethmoid – transmit CN I nerves to olfactory bulbs of the brain MIDDLE CRANIAL FOSSA Central part is composed of sella turcica on the body of the sphenoid and large, depressed lateral parts on each side Separated from anterior fossa by sphenoidal crests laterally and sphenoidal limbus centrally 1. Sphenoidal crests are formed by posterior borders of the lesser wings of sphenoid bones 2. Sphenoidal crests end in anterior clinoid processes 3. Limbus of sphenoid forms anterior boundary of the transversely oriented prechiasmatic sulcus extending between right and left optic canals Boundary between the middle and posterior cranial fossae is the superior border of the petrous part of the temporal bone laterally and the dorsum sellae of the sphenoid medially Sella turcica is the saddle-like bony formation on the upper surface of the sphenoid, surrounded by anterior and posterior clinoid processes 1. Surround the hypophyseal fossa—bed of the pituitary gland 2. Sella turcica is composed of 3 parts 1. Tuberculum sellae—median elevation forming the posterior boundary of the prechiasmatic sulcus and the anterior boundary of the hypophysial fossa 2. Hypophysial fossa (pituitary fossa)—median depression in the body of the sphenoid that accommodates the pituitary gland 3. Dorsum sellae—square plate of bone projecting superiorly from the body of the sphenoid Forms the posterior boundary of the sella turcica and its prominent superolateral angles make up the posterior clinoid processes On each side of the body of the sphenoid, CRESCENT OF FOUR FORAMINA 1. Superior orbital fissure Located between the greater and lesser wings—opens anteriorly into the orbit 2. Foramen rotundum o o Runs a horizontal course to an opening on the anterior aspect of the root of the greater wing of the sphenoid into a bony formation between the sphenoid, the maxilla, and the palatine bones, the PTERYGOPALATINE FOSSA 3. Foramen ovale Opens inferiorly into the infratemporal fossa 4. Foramen spinosum Opens into infratemporal fossa in relationship to the spine of the sphenoid Foramen lacerum o Not part of the crescent of foramina o Is an artifact of dried cranium o Lies posterolateral to the hypophysial fossa o Closed by cartilage plate in life o Internal carotid artery and its accompanying sympathetic and venous plexuses pass across the superior aspect of the cartilage and some nerves traverse it horizontally, passing to a foramen in its anterior boundary Groove for greater petrosal nerve o Extending posteriorly and laterally from foramen lacerum is this on the anterosuperior surface of the petrous temporal bone o There is also a small groove for lesser petrosal nerve POSTERIOR CRANIAL FOSSA Largest and deepest of the 3 fossae lodges cerebellum, pons, and medulla oblongata Formed mostly by occipital bone Dorsum sellae of the sphenoid marks its anterior boundary centrally Petrous and mastoid parts of temporal bones contribute to its anterolateral walls Clivus o Marked incline from dorsum sellae Internal occipital crest partly divides the fossa into cerebellar fossae o Ends in internal occipital protuberance formed in relationship to the confluence of the sinuses Jugular foramen is at the base of the petrous ridge of the temporal bone o Transmits sigmoid sinus and several cranial nerves Anterosuperior to the jugular foramen is the internal acoustic meatus for the facial and vestibulocochlear nerves (CN VIII) and labyrinthine artery Hypoglossal canal for hypoglossal nerve is superior to the anterolateral margin of the foramen magnum WALLS OF CRANIAL CAVITY Squamous part of temporal bone is fairly thin—usually places of skull covered by muscles are thinner Most bones of calvaria consist of internal and external tables of compact bone, separated by diploe. Diploe is cancellous bone containing red bone marrow during life, through which run canals formed by diploic veins Internal table of bone is thinner than the external table Some areas have only a thin plate of compact bone with no diploe Walls are buttressed in some places to stand up to the tension forces produced by muscles of mastication FRONTONASAL BUTTRESS o Extends from region of canine tooth between the nasal and orbital cavities to the central frontal bone ZYGOMATIC ARCH—LATERAL ORBITAL MARGIN BUTTRESS o From region of the molars to the lateral frontal and temporal bones OCCIPITAL BUTTRESSES o Regions o o o o Transmit forces received lateral to the foramen magnum from the vertebral column of head Face is divided into 8 regions Names of the regions correspond to the underlying bones Frontal, parietal, occipital, temporal, and mastoid regions Viscerocranial portion of the head includes facial region, divided into five bilateral and three median regions related to superficial features (oral and buccal regions), to deeper soft tissue formations (parotid region), and to skeletal features (orbital, infra-orbital, nasal, zygomatic, mental regions)