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Chapter 4

White Chapter 4 - Skull: Cranium and Mandible

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University of Toronto Mississauga
Carolan Wood

NotesFromReadingCHAPTER4SKULLCRANIUMANDMANDIBLEPGS4399IntroductionMost bones of the skull base lie underneath the brain and are at least partly preformed in cartilage The facial bones and bones of the roof and sides of the skull are dermal bones formed in sheets of connective tissue under the skinThe earliest jaws ere derived from the first or mandibular gill arch The skull is one of the keys to aging sexing and understanding the evolutionary history of hominidsIt forms the bony foundation for a the senses of sight smell taste and hearing Houses and protects the brainThe skull forms the framework of the chewing apparatusOrbitsthe eye socketsAnterior Nasal Aperture or Piriform ApertureThe hole between and below the orbits the nose holeExternal Acoustic MeatiEar holesForamen MagnumThe large oval hole in the base of the skullZygomatic ArchesThe thin bony bridges at the skids of the skullHandling the SkullThe skull should be handled above a padded surface and stabilized against rolling on the surface by means of sandbags or cloth rings designed for this purposeA finger or thumb placed in and behind the foramen magnum will not damage the bone but other openings such as the orbits or zygomatic arches are more fragile and should never be used as gripping surfacesDelicate parts that are susceptible to damage during cranial manipulation include the edges and insides of the nasal aperture as well as the thin projecting ptertygoid plates and styloid processes at the base of the skullElements of the SkullSkull is the entire bony framework of the head including the lower jawMandible is the lower jawCranium is the skull without the mandibleCalvaria or calvarium is the cranium without the faceCalotte is the calvaria without the baseSplanchnocranium is the facial skeletonNeurocranium is the braincase The anterior middle and posterior cranial fossae are respectively occupied by the frontal lobes temporal lobes and cerebellum of the brain When the ear ossicles three pairs of tiny bones associated with hearing are included and the hypoid excluded there are usually 28 bones in the adult human skull Distinguishing these bones is occasionally made difficult because some of them fuse together during adult life best to begin studying with young adult specimens where bones are recongizableThere are often sutural bones also called Wormian bones or extrasutural bones which are irregular ossicles that occur along some sutures A large triangular inca bone is occasionally found at the rear of human crania Growth and Architecture Sutures and Sinuses In early vertebrates two kinds of bone evolved dermal bone and cartilagereplacement boneNotesFromReadingCHAPTER4SKULLCRANIUMANDMANDIBLEPGS4399Dermal bones form the sides and roof of the skull and make up the facial skeletonThe bones of the cranial base known as the basicranium are mostly preformed in cartilage the ethmoid bone surrounds the olfactory apparatus and nerves the sphenoid bone surrounds the optic nerves the temporal bones surround the auditory system and the occipital bone surrounds the spinal cord The remaining bones in the skull mandible greater wings of the sphenoid ear ossicles hyoid are derived from the gill arches of primitive vertebratesAt birth the skull is made up of 45 separate elements and is large relative to other parts of the body In the adult skull the skull bones contact along joints with interlocking sawtooth or zipperlike articulations called suturesZygomaticomaxillary sutures are sutures between the zygomatics and maxillae and frontonasal sutures are short sutures between the frontal and nasals Sagittal suture passes down the midline between the parietal bonesMetopic or frontal suture passes between unfused frontal halves and only rarely persists into adulthoodCoronal suture lies between the frontal and parietals Lambdoid or lambdoidal suture passes between the two parietals and the occipitalSquamous sutures are unusual scalelike bevelled sutures between temporal and parietal bonesBasilar suture lies between the sphenoid and the occipital Parietomastoid suturespass between the parietals and the temporals constituting posteriorextensions of the squamous sutureOccipitomastoid suture pass between the occipital and temporals on either side of the vaultBefore adulthood several of these sutures are preformed as synchondrosessemirigid joints made with hyaline cartilage These synchondroses are temporary and will eventually be replaced either by syndesmosesrigid ligamentous jointsor by bony fusionSphenooccipital Synchondrosis preceds the basilar sutureSphenopetrosal Synchondrosis proceeds the sphenotemporal suturePetroocchondrosis marks the site of future fusion of the squamous and lateral portions of the occipital boneAnterior intraoccipital synchondrosis marks the site of future fusion of the basilar and lateral portions of the occipital bonesSphenoethmoidal synchondrosis precedes the sphenoethmodial suture At birth the cranial vault has six areas which instead of being covered by bone are covered by dense connective tissue between plates of bone Frontanelle are cartilaginous membranes that eventually harden and turn to bone The anterior and posterior fontanelles are single along the midline at either end of the sagittal sutureThe mastoid and sphenoidal fontanelles are paired with one of each on the right and left sides of the cranium Sinuses are void chambers in the cranial bones that enlarge with the growth of the face There are four basic sets of sinuses one each in the maxillae frontal ethmoid and sphenoidSkull Orientation The Frankfurt Horizontal is a plane defined by three points the right and left portion points located at the top of each external acoustic meatus and the left orbitale located at the bottom of the left orbitSkulls are normally viewed from five standard perspectives all in Frankfurt Horizontal
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