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General Features of the Skull
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Terms in this set (77)
Maxillary bone:
• Paired & can be seen when the mandible is removed

Hard Palate:
• Palatine bones form the posterior 1/3
- Posterior choanae (= posterior nasal aperture, "choane" = funnel, opening between the nasal cavity and the nasopharynx)
• (2/3 anterior is formed by maxilla bones)

Zygomatic Arch:
• Zygomatic process of the temporal bone (more posterior)
• Temporal process of the zygomatic bone (more anterior)

Temporal Bone:
• lies lateral
• mastoid & styloid processes can be seen

Foramen magnum:
• Occipital bone
• Allows passage of the brainstem as it becomes the spinal cord
• Bordered on either side by the
occipital condyles
- Articulate with C1
Image: Base of the Skull
• Only be seen after the removal of the calvaria, brain & dura

Base of the internal Aspect:
• Frontal, ethmoid (anterior), sphenoid (middle), temporal, & occipital bones

* Note the grooves in the parietal and temporal bones for the middle meningeal artery leading to foramen spinosum

Floor divided 3 cranial fossae:
• Anterior = frontal bone, ethmoid bone, & parts sphenoid bone
• Middle = "butterfly-shaped", the sphenoid bone & two temporal bones
• Posterior =occipital bone, the two temporal bones, & parietal bones
Image: Internal of the Skull
Other Bones of the Skull• Vomer (=thin plate of bone forming the posteroinferior part of the nasal septum) • Ethmoid - Crista Galli- attaches part of the dura • Inferior Nasal Conchae (AKA Turbinate, or Turbina) • Nasal Bones • Palatine • Lacrimal (more anterior than orbital plate of ethmoid) • Ear ossiclesFrontal Bone• Forms the forehead • Forms the roof of the orbits (eye sockets) • Frontal bone articulates with the parietal bones at the coronal suture • Sinuses located within the frontal bone (above, medial to orbits) • Glabella- between the orbits • Supraorbital foramen/notchParietal Bones• Form the walls of the calvaria Two Curved lines -- Outside: • Superior Temporal Line: - Attachment of the temporal fascia • Inferior Temporal Line: - Beginning Origin of temporalis muscle • Temporal FossaParietal Bones: Newborns• Two parietal bones meet in the mid-line at the sagittal suture • Anterior and posterior fontanelles (soft spots) Anterior Fontanelle: • Soft spot in infants is the where the sagittal & coronal sutures meet • will become Bregma Posterior fontanelle: • Parietal bones meet w/ lambdoidal suture posteriorly • will become lambdaTemporal Bones• Form part of lateral aspect of skull in addition to cranial vault • Includes mastoid and styloid processes (most anterior) • Zygomatic process • Groove for middle meningeal artery • Forms internal, external meatii (meatus) - Contains middle, inner ear (= external/internal acoustic meatus)Sphenoid BoneLocation: • at the base of the skull anterior to the temporal bone - is unpaired (= an irregularly shaped bone forming the central portion of the skull) Articulates with 8 bones: • Frontal, parietal, temporal, occipital, vomer, zygomatic, palantine, ethmoid Structure: • Body = contains a left and right sinus (AKA sphenoid sineses) - Sinuses are hollows in bones - Rapid growth; Lighten skull; Phonation; Doctor$ ???? - Superior surface of the body features the Sella Turcica * Note: hypophyseal fossa (within sella turcica) that houses the pituitary gland • Greater and lesser wings • Pterygoid processes = outside the skull w/ a lateral & medial pterygoid plate for muscle attachmentSphenoid Bone: Sphenoid Foramina• Optic foramen • Superior orbital fissure - (underneath the lesser wing) • Foramen rotundum • Foramen ovale • Foramen spinosum • Foramen lacerum? (junction of several bones) - Sphenoid, temporal, and occipitalOccipital Bone• Forms much of the base of the posterior aspect • Unpaired • Occipital condyles - Articulation w/ C1 vertebra Foramen: • Foramen magnum -CN XI (11) and vertebral aa. enter skull - Spinal cord exits • Hypoglossal canals - (old name was anterior condyloid foramen) - CN XII (12) • Foramen lacerumFacial SkeletonMostly formed by the: • Paired Zygomatic • Maxilla(e) • Paired Nasal • Mandible • Nasal CartilagesMaxillae• Paired bones that form the facial skeleton between the mouth and the eyes (orbits) • Join the mid-line at the intermaxillary suture • Palatine process of each maxilla meet to form the hard palate (ant. 2/3) • Houses the upper teeth • Incisive fossa/foramenMaxillae ForaminaInfraorbital: • Groove • Canal • Foramen • infraorbital groove in maxillary bone projects via the infraorbital canal to the infraorbital foramen. • located approximately 1cm inferior to the infraorbital margin • Incisive (ant. on hard plate) • Inferior orbital fissure = situated between maxilla & sphenoid bones; superior orbital fissure is part of sphenoid boneMaxillae Sinus• Large maxillary sinus is within the body of each maxillaMandible• Considered the strongest bone of the face • It forms the lower jaw and is the moveable part Structure: • Central body • paired vertical rami • Angle = point at which the body meets a ramus • Superiorly the ramus has a condylar process posteriorly, coronoid process anteriorly - Coronoid and condylar processes are separated by the mandibular notch • Mental spines posteriorly • Ridge on inside of body mylohyoid line; attachment of the mylohyoid muscle • Mental foramina in ramus of the mandible projects the mental nerve from the inferior alveolar nerve (branch of trigeminal CNV...aka V3)Zygomatic Bones• Form the prominences of the cheeks (cheekbones) • Forms the anterolateral rims of the orbits • Forms much of the infraorbital margins of the orbit • Articulate medially with the greater wing of the sphenoid, superiorly w/ frontal • Temporal process unites with the zygomatic process of the temporal bone to form the zygomatic archEthmoid Bone• Unpaired - hidden except for the portion that projects into the anterior fossa • Ethmoid Sinuses - anterior, middle, posterior air cells • Cribriform Plate • Olfactory Nerve • Forms superior and middle nasal conchae • Inferior conchae- (palatine bone) • Crista Galli projects into anterior cranial fossaAnterior Cranial Fossa• Cribriform plate: Axons of olfactory cells in olfactory epithelium that form olfactory nerves • Optic foramen (tweener): Optic nerves (CN II) & ophthalmic arteriesMiddle cranial fossa• Superior orbital fissure (sphenoid): Ophthalmic veins; ophthalmic nerve (CN V1); CN III, IV, & VI; & sympathetic fibers • Foramen rotundum (sphenoid): Maxillary nerve (CN V2 ) • Foramen ovale (sphenoid): Mandibular nerve (CN V3) & accessory meningeal artery • Foramen spinosum (sphenoid): Middle meningeal artery & vein & meningeal branch of CN V3 • Foramen lacerum (sphenoid, temporal, & occipital): Deep petrosal nerve & some meningeal arterial branches & small veins • Carotid canal (temporal): internal carotid arteries, deep petrosal nerve***Posterior cranial fossa• Internal auditory meatus (temporal): ** • Jugular foramen (temporal): CN IX, X, and XI; superior bulb of internal jugular vein; inferior petrosal and sigmoid sinuses; & meningeal branches of ascending pharyngeal and occipital arteries • Stylomastoid foramen (temporal): ** • Hypoglossal canal (occipital): Hypoglossal nerve (CN XII) • Foramen magnum (occipital): Medulla and meninges, vertebral arteries, CN XI, dural veins, anterior and posterior spinal arteriesBrain: Cerebrum (Lat)Lobes: • Frontal Lobe • Parietal Lobe • Temporal Lobe • Occipital Lobe Sulci/Gyri: • Central Sulcus • Pre and Post Central gyri • Lateral Sulcus • Superior. Middle, and inferior temporal gyriBrain: Cerebrum (Med)Lobes: • Frontal Lobe • Parietal Lobe • Temporal Lobe • Occipital Lobe Sulci/Gyri/etc.: • Parieto-occipital sulcus • Central sulcus • Cingulate sulcus • Corpus Collosum • (4 parts: genu, rostrum, trunk, splenium)Brain: Cerebrum (inf)Lobes: • Frontal Lobe • Parietal Lobe • Temporal Lobe • Occipital Lobe Poles: • Frontal pole • Temporal pole • Occipital pole Other: • Hypophysis (pituitary gland)- endocrine control (not seen on cadaver brains...as it is left in the sella turcica • Mammillary bodies- limbic system Midbrain: • Red nucleus-mtr coord • Substantia Nigra-mvmt and coordination (Parkinson's Dz)Brainstem / CerebellumBrainstem: • Pons • Cerebral peduncle • Medulla oblongata Cerebellum Thalamus 3rd and 4th Ventricles: • choroid plexi Cerebral Aqueduct (of Sylvius): • Connects 3rd and 4th ventriclesGeneral Cranial Nerves• There are 12 pairs of cranial nerves • There are some that are purely sensory, some are voluntary motor, some are mixed, and some contain autonomic (involuntary parasympathetic) motor fibers • The cranial nerves that contain sensory and parasympathetic fibers typically have Ganglia, collections of nerve cells located outside the central nervous system, that give rise to these sensory fibers • A Ganglion is a collection of neuron cell bodies outside the CNS. • Unlike spinal nerves, the motor and sensory fibers of the cranial nerves do not necessarily form different roots, but are mixed together in a single nerve12 Cranial NervesI. Olfactory - (Sensory) II. Optic - (Sensory) III. Oculomotor - (Motor) IV. Trochlear- (Motor) V. Trigeminal - (Both) VI. Abducens - (Motor) VII. Facial- (Both) VIII. Vestibulocochlear- (Sensory) IX. Glossopharyngeal- (Both) X. Vagus- (Both) XI. Spinal Accessory- (Motor) XII. Hypoglossal- (Motor) *Some Say Marry Money But My Brother Says Big Brains Matter More * On Occasion Our Trusty Truck Acts Funny, Very Good Vehicle Any HowI. Olfactory (Some)• Sensory nerve of smell (olfaction) • Fibers enter the nasal cavity --> exist through the cribiform plate Structure: • Olfactory bulb, tract extension of the CNS (forebrain)II. Optic (Say)• Sensory nerve of vision - afferent (sensory) limb of pupillary light reflex • O: retina (retinal ganglion cells = axons of cells) --> optic disc & form Optic N. --> optic chiasm • Exist: optic foramen ** not a nerve --extension of the central nervous system - ganglion cells give rise to its fibers, & are part of the retina - 'nerve' is covered by the meninges & technically a tractII. Optic: Optic chiasmOptic chiasm (= X-shaped structure): - Fibers from the medial sides of the retinas cross to the opposite side @ chiasm - Fibers from the lateral side stay on that side • Lateral visual field = projects to the medial retinal field • Medial visual field = projects to the lateral retinal field - Each medial retinal field signals cross through the chiasm to join the Lateral retinal fieldII. Optic: Damage• Bitemporal Hemianopia = pituitary tumors cause damage to the optic chiasm & therefore loss of the lateral visual fields (medial retinal fields) and present as tunnel vision • Age-related Macular Degeneration (AMD) (central retinal deterioration) = lead to loss of central vision and visual acuityIII. Oculomotor (Marry)• Motor nerve of voluntary muscles of the orbit, moving the eyeball & raising the upper lid - efferent limb of pupillary light reflex • Innervates 5 out of 7 skeletal muscles of the eye: - Levator Palpebrae Superioris (rising eyelid) - Superior Rectus - Inferior Rectus - Medial Rectus - Inferior Oblique EXCEPT: superior oblique (CN IV) & lateral rectus (CN VI)III. Oculomotor (Marry): Parasympathetic nerves1st of Parasympathetic N. (3,7,9,10) Autonomic motor fibers: • constricting the pupil • accommodation of the lens for close-up vision. • O: midbrain - Presynaptic in midbrain - Postsynaptic ciliary ganglion • Enters the orbit through the superior orbital fissureIV. Trochlear (Money)• Motor nerve of voluntary muscles of the eye - NS: Superior Oblique • Only CN to originate on the dorsum of the Midbrain • Exist: superior orbital fissureV. Trigeminal (But)• Sensory = primarily to skin of the head, face, & teeth • Motor = primarily is to muscles of mastication 3 important divisions (branches): 1) Ophthalmic Nerve (V1) 2) Maxillary Nerve (V2) 3) Mandibular Nerve (V3) • O: PonsThree Branches of Trigeminal: Ophthalmic Nerve (V1)• passes through superior orbital fissure (along with CN III and CN IV and CN VI); supplies sensory innervation to the forehead (ant. 2/3 of scalp), upper eyelid, dorsum of the nose, eyeball, anterior nasal cavity & most sinuses (all sinuses except the maxillary sinuses) • Gives rise to the supraorbital nerve • Afferent limb of corneal reflex • From nasociliary branch Note: all sensory fibers of V arise from trigeminal ganglionThree Branches of Trigeminal: Maxillary Nerve (V2)• passes through the foramen rotundum, then crosses the inferior orbital fissure - it provides sensation to the lower lid, nasal cavity, palate, upper teeth, maxillary sinus, side of the nose, upper lip, and upper part of the cheek • Afferent limb of sneeze reflex • Gives rise to the infraorbital nerveThree Branches of Trigeminal: Mandibular Nerve (V3)• exits skull through foramen ovale, only branch with voluntary motor fibers, provides gen. sense to anterior 2/3 of tongue, lower teeth, cheek. Lower lip and skin overlying mandible • Motor to muscles of mastication (temporalis, masseter, medial and lateral pterygoid), and 2 "T" muscles (tensor tympani and tensor veli palatini...not cricital) • Afferent & efferent limbs of jaw jerk reflex • Gives rise to (sensory) buccal, lingual, inferior alveolar, auricolotemporal and (motor) mylohyoid nervesVI. Abducens (My)• Supplies only one muscle (motor) • It supplies the lateral rectus of the eye (abductor) • Leaves brain between pons & medulla; near the midline • Exits the skull through the superior orbital fissureVII. Facial Nerve (Brother)2nd of Parasympathetic N. (3,7,9,10) • Both motor and sensory- one of the most complex of the cranial nerves • Supplies the voluntary muscles of the face (muscles of facial expression) and the scalp and platysma muscle. • The best documented sensory fibers of the facial nerve are those that carry taste from the anterior 2/3rds of the tongue • Originates at junction of pons w/ medulla • Exits the skull through the stylomastoid foramen (via internal auditory meatus, facial canal) • Efferent limb of corneal reflex-(touch cornea=blink); Afferent limb is V1)• Visceral Motor • Presynaptic in pons • Postsynaptic in pterygopalatine and submandibular ganglia • Parasympathetic Innervation of submandibular and sublingual salivary glands, lacrimal gland, and glands of nose and palate • Efferent limb of corneal reflex; (Afferent limb is V1)• Facial nerve Summary:• Muscles of facial expression • Autonomics to the glands (e.g., submandibular and sublingual salivary glands, lacrimal gland, and glands of nose and palate) • Taste to anterior 2/3 of the tongue (chorda tympani); (taste for posterior 1/3 is provided by glossopharyngeal nerve (CN IX); (V3 provides general sense to the tongue) • Efferent for the corneal reflexVIII. Vestibulocochlear (Says)Sensory - Two parts: 1) cochlear root = cochlear (Spiral) ganglion- fibers come from the apparatus in the ear responsible for hearing 2) vestibular root = vestibular ganglion- fibers go the apparatus in the ear responsible for balance • O: Medulla • Exits: internal auditory meatusIX. Glossopharyngeal (Big)• Sensory: pharynx and larynx, middle ear, gen. sense & taste from post. 1/3 of tongue • Motor: stylopharyngeus muscle (voluntary) • Action: Aids in swallowing by elevating the pharynx • O: Medulla (posterior to the vestibulocochlear nerve) • Exists: jugular foramen • It has superior and inferior gangliaIX. Glossopharyngeal: Parasympathetic3rd of Parasympathetic N. (3,7,9,10) Visceromotor: • Presynaptic in medulla (inf. salivatory nucleus) • Postsynaptic otic ganglion • NS (parasympathetic) parotid gland Visceral Sensory: • Sensation from parotid gland, carotid body & sinus, pharynx, & middle ear Reflexes: • Afferent limb = gag reflexX. Vagus (Brains)• Motor nerve to pharynx, larynx • Sensory nerve to larynx • Action: - Parasympathetic to thoracic viscera (=heart, pericardium [=a membrane, or sac, that surrounds your heart], lungs, pleura, thymus, & esophagus) - Parasympathetic to abdominal viscera (=stomach, small & large intestine, liver, gallbladder & pancreas) down to splenic flexure of transverse colon • O: medulla • Exits: jugular foramenX. Vagus: Parasympathetic4th of Parasympathetic N. (3,7,9,10) • The vagus (wanderer) has branches in the neck, thorax (lungs, heart, esophagus), & in the abdomen (stomach, liver, small intestine, proximal 2/3 of colon) • Has a superior & inferior ganglion • Contains sensory fibers for both pain and reflexes Reflexes: • Afferent = cough reflex • Efferent limb = sneeze reflex, gag reflex, & cough reflexXI. Spinal Accessory (Matter)• Motor nerve to sternocleidomastoid & trapezius (two voluntary muscles) = head-turning • O: spinal cord, medulla • Enters: foramen magnum • Exits: jugular foramen (posterior to the vagus nerve)XII. Hypoglossal (Money)• Motor nerve to skeletal muscles of the tongue • O: Medulla between pyramid & olive • Exist: hypoglossal canalReflexes- SummaryVertebral ArteryRIGHT: • Right Vertebral A. (after Common Carotid) <-- Right Subclavian artery (1st Part) <-- Brachiocephalic A.<-- Aortic Arch LEFT: • Left Vertebral A. <-- Left Subclavian A. <-- Aortic Arch • Occasionally (on left) arises directly from aortic arch Beginning to End: • Enters transverse vertebral foramina, beginning at C6 (not C7) • Travels superiorly through C1, leaves the transverse foramen & runs medially superior on the "groove/sulcus for vertebral artery" on the posterior arch • Makes a right angle bend superiorly through foramen magnum to the cranium where both sides join to form the basilar artery (Circle of Willis)Circle of WillisSTART TO END: • Vertebral Arteries: • Post. Inf. Cerebellar arteries (PICA) • Basilar artery • Basilar artery (ventral midline of the brainstem): - anterior inferior cerebellar arteries - superior cerebellar arteries - Posterior cerebral arteries • Posterior cerebral arteries: - Posterior communicating arteries (@ border of the pons & midbrain) --> middle cerebral arteries (off Internal Carotid) --> ant. cerebral a. • Anterior cerebral arteries (off internal carotid): - connected by a single anterior communicating artery * Note: Oculomotor nerve always exits between the posterior cerebral and superior cerebellar arteriesInternal Carotid ArteryRIGHT: • Inter. Carotid A. (upper level of thyroid cartilage) <-- Right common carotid a. <-- Brachiocephalic A. <-- Aorta LEFT: • Inter. Carotid A. (upper level of thyroid cartilage) <-- Left common carotid a. <-- Aorta Towards the End: • No branches in the neck • Ascends in carotid sheath (= common carotid artery; parts of internal carotid artery & external carotid artery; internal jugular vein; vagus nerve; part of recurrent laryngeal nerve; deep cervical lymph nodes) • Enters middle cranial fossa (butterfly) through carotid canal • ENDS = dividing into anterior and middle cerebral arteriesCirculus Arteriosis or "Circle of Willis" (proper)= a large arterial anastomosis that unites the internal carotid and vertebrobasilar arterial systems to produce collateral blood flow around vital structures at the base of the brain "Circle of Willis" Arteries: • R and L Posterior cerebral a. • R and L Post. communicating a. • R and L Internal carotid a. • R and L Anterior cerebral a. • Anterior communicating a *Note: this anastomosis is fairly variable.Dural Venous Drainage• Superior sagittal sinus (runs in the superior portion of the falx cerebri) • Inferior sagittal sinus (runs in the inferior portion of the falx cerebri) • Great cerebral vein drain into the straight sinus • Straight sinus + superior sagittal sinus join & drain via the transverse sinus (which runs in the tentorium cerebelli) • Superior petrosal sinus (which comes from cavernous sinus) & Transverse sinus drains into the sigmoid sinus • Sigmoid sinus drains into the internal jugular vein and courses inferiorly through the neckDural Venous Drainage -• Cavernous sinus drains orbit & anterior structures • Cavernous sinus is related to structures including: - CN III - CN IV - CN VI - CN V1 - CN V2 - Internal Carotid artery - Pituitary - Optic chiasmHead of Injuries (pg 1359 Moore)• Head injuries are a major cause of death and disability. The complications of head injuries include hemorrhage, infection, and injury to the brain (e.g., concussion) and cranial nerves. Disturbance in the level of consciousness is the most common symptom of head injury. Almost 10% of all deaths in the United States are caused by injury, and approximately half of traumatic deaths involve the brain (Louis et al., 2022). Head injuries occur mostly in young persons between the ages of 15 and 24 years. The major cause of brain injury varies; however, motor vehicle and motorcycle accidents are prominent. The high energy transmitted during these accidents can cause fiber tracts and axons within the brain to shear, causing a pattern called "diffuse axonal injury" for which there is no good treatment.Headaches/Facial Pain (pg Moore)• Few complaints are more common than headaches and facial pain. Although usually benign and frequently associated with tension, fatigue, or mild fever, headaches may indicate a serious intracranial problem such as a brain tumor, subarachnoid hemorrhage, or meningitis. Neuralgias (G. algos, pain) are characterized by severe throbbing or stabbing pain along the course of a nerve caused by a demyelinating lesion. They are a common cause of facial pain. Terms such as facial neuralgia describe diffuse painful sensations. Localized aches have specific names, such as earache (otalgia) and toothache (odontalgia). A sound knowledge of the clinical anatomy of the head helps in understanding the causes of headaches and facial pain.Injury to the Superciliary Arches• The superciliary arches are relatively sharp bony ridges (see Fig. 8.3). Consequently, a blow to them (e.g., during boxing) may lacerate the skin and cause bleeding. Bruising of the skin surrounding the orbit causes tissue fluid and blood to accumulate in the surrounding connective tissue, which gravitates, usually unilaterally, into the superior (upper) eyelid and around the eye ("black eye")Malar Flush• The zygomatic bone was once called the malar bone; consequently, you are likely to hear the clinical term malar flush. This redness of the skin covering the zygomatic process (malar eminence) is associated with a rise in temperature in various fevers occurring with certain diseases, such as tuberculosis. A characteristic "butterfly rash" is seen over the zygomatic eminence in some cases of systemic lupus erythematosus disease, an autoimmune disease.Fractures of the Maxillae and Associated Bones• Dr. Léon-Clement Le Fort (a Paris surgeon and gynecologist, 1829-1893) classified three common variants of fractures of the maxillae (Fig. B8.1): • Le Fort I fracture: wide variety of horizontal fractures of the maxillae, passing superior to the maxillary alveolar process (i.e., to the roots of the teeth), crossing the bony nasal septum and possibly the pterygoid plates of the sphenoid • Le Fort II fracture: passes from the posterolateral parts of the maxillary sinuses (cavities in the maxillae) superomedially through the infra-orbital foramina, lacrimals, or ethmoids to the bridge of the nose. As a result, the entire central part of the face, including the hard palate and alveolar processes, is separated from the rest of the cranium. • Le Fort III fracture: horizontal fracture that passes through the superior orbital fissures and the ethmoid and nasal bones and extends laterally through the greater wings of the sphenoid and the frontozygomatic sutures. Concurrent fracturing of the zygomatic arches causes the maxillae and zygomatic bones to separate from the rest of the cranium.Resorption of Alveolar Bone• Extraction of teeth causes the alveolar bone to resorb in the affected region(s) (Fig. B8.3). Following complete loss or extraction of maxillary teeth, the tooth sockets begin to fill in with bone, and the alveolar process begins to resorb. Similarly, extraction of mandibular teeth causes the bone of the alveolar part to resorb. Gradually, the mental foramen comes to lie near the superior border of the body of the mandible (Fig. B8.3A-C). In some cases, the mental foramina disappear, exposing the mental nerves to injury. Pressure from a dental prosthesis (e.g., a denture resting on an exposed mental nerve) may produce pain during eating. Loss of all the teeth results in a decrease in the vertical facial dimension and mandibular prognathism (overclosure). Deep creases in the facial skin also appear that pass posteriorly from the corners of the mouth. •Fractures of the Calvaria• The convexity of the calvaria distributes and thereby usually minimizes the effects of a blow to the head. However, hard blows in thin areas of the calvaria are likely to produce depressed fractures, in which a bone fragment is depressed inward, compressing and/or injuring the brain (Fig. B8.4). Linear calvarial fractures, the most frequent type, usually occur at the point of impact, but fracture lines often radiate away from it in two or more directions. In comminuted fractures, the bone is broken into several pieces. If the area of the calvaria is thick at the site of impact, the bone may bend inward without fracturing. However, a fracture may occur some distance from the site of direct trauma where the calvaria is thinner. In a contrecoup (counterblow) fracture, no fracture occurs at the point of impact, but one occurs on the opposite side of the cranium.Fractures of the Mandible• A broken mandible usually involves two fractures, which frequently occur on opposite sides of the mandible. Therefore, if one fracture is observed, a search should be made for another (e.g., a hard blow to the jaw often fractures the neck and body of the mandible in the region of the opposite canine tooth). Fractures of the coronoid process of the mandible are uncommon and usually single (Fig. B8.2). Fractures of the neck of the mandible are often transverse and may be associated with dislocation of the temporomandibular joint (TMJ) on the same side. Fractures of the angle of the mandible are usually oblique and may involve the bony socket or alveolus of the 3rd molar tooth (Fig. B8.2, line C). Fractures of the body of the mandible frequently pass through the socket of a canine tooth (Fig. B8.2, line D).Surgical access to Cranial Cavity• Surgeons access the cranial cavity and brain by performing a craniotomy, in which a section of the neurocranium, called a bone flap, is elevated or removed (Fig. B8.5). Because the adult pericranium (periosteum of cranium) has poor osteogenic (boneforming) properties, little regeneration occurs after bone loss (e.g., when pieces of bone are removed during repair of a comminuted cranial fracture). Surgically produced bone flaps are put back into place and wired to other parts of the calvaria or held in place temporarily with metal plates. Reintegration is most successful when the bone is reflected with its overlying muscle and skin so that it retains its own blood supply during the procedure and after repositioning. If the bone flap is not replaced (i.e., a permanent plastic or metal plate replaces the flap), the procedure is called a craniectomy.Development of the Cranium **• The bones of the calvaria and some parts of the cranial base develop by intramembranous ossification. Most parts of the cranial base develop by endochondral ossification. At birth, the bones of the calvaria are smooth and unilaminar; no diploë is present. The frontal and parietal eminences are especially prominent (Fig. B8.6). The cranium of a neonate is disproportionately large compared to other parts of the skeleton; however, the facial aspect is small compared to the calvaria, which forms approximately one eighth of the cranium. In the adult, the facial skeleton forms one third of the cranium. The large size of the calvaria in infants results from precocious growth and development of the brain and eyesThe mandible is the most dynamic of our bones; its size and shape and the number of teeth it normally bears undergo considerable change with age. In the neonate, the mandible consists of two halves united in the median plane by a cartilaginous joint, the mandibular symphysis. Union between the halves of the mandible is affected by means of fibrocartilage. This union begins during the 1st year, and the halves are fused by the end of the 2nd year. The body of the mandible in neonates is a mere shell lacking an alveolar part with each half enclosing five deciduous teeth. These teeth usually begin to erupt in infants at approximately 6 months of age. The body of the mandible elongates, particularly posterior to the mental foramen (Fig. B8.2), to accommodate this development. Later, eight permanent teeth begin to erupt during the 6th year of life (Fig. B8.8). Eruption of the permanent teeth is not complete until early adulthood.Age changes• As people age, the cranial bones normally become progressively thinner and lighter, and the diploë gradually becomes filled with a gray gelatinous material. In these individuals, the bone marrow has lost its blood cells and fat, giving it a gelatinous appearance.Obliteration of Cranial Suture• The obliteration of sutures between the bones of the calvaria usually begins between the ages of 30 and 40 years on the internal surface. Approximately 10 years later, the sutures on the external surface obliterate (Fig. B8.10; cf. Fig. 8.8B). Obliteration of sutures usually begins at the bregma and continues sequentially in the sagittal, coronal, and lambdoid sutures. Closure times vary considerably.Craniosynostosis and cranial malformations• Premature closure of the cranial sutures (primary craniosynostosis) results in several cranial malformations (Fig. B8.11). The incidence of primary craniosynostosis is approximately 1 per 2,000 births (Kliegman et al., 2020). The cause of craniosynostosis is unknown, but genetic factors appear to be important. The prevailing hypothesis is that abnormal development of the cranial base creates exaggerated forces on the dura mater (outer covering membrane of the brain) that disrupt normal cranial sutural development. These malformations are more common in males than in females and are often associated with other skeletal anomalies. The type of malformed cranium that forms depends on which sutures close prematurely. Premature closure of the sagittal suture, in which the anterior fontanelle is small or absent, results in a long, narrow, wedge-shaped cranium, a condition called scaphocephaly (Fig. B8.11A). When premature closure of the coronal or the lambdoid suture occurs on one side only, the cranium is twisted and asymmetrical, a condition known as plagiocephaly (Fig. B8.11B). Premature closure of the coronal suture results in a high, tower-like cranium, called oxycephaly or turricephaly (Fig. B8.11C). The latter type of cranial malformation is more common in females. Premature closure of sutures usually does not affect brain development.