The Skull
Cranium:
Anterior View: includes the frontal bone, zygomatic bones, nasal bones, maxilla, and mandible
Lateral View: includes lateral calvaria bones, lateral facial bones, and the mandible
Superior View: includes frontal, parietal, and occipital bones
Inferior View: includes maxilla, zygomatic, palatine, sphenoid, temporal, and occipital bones
External Foramina:
Foramen Bone Contents Supra-orbital foramen Frontal Supra-orbital nerve and vessels Infra-orbital foramen Maxillary Infra-orbital nerve and vessels Mental foramen Mandible Mental nerve and vessels Zygomaticofacial foramen Zygomatic Zygomaticofacial nerve Parietal foramen Parietal Emissary veins Incisive foramen Maxilla Nasopalatine nerve, sphenopalatine vessels Greater palatine foramen Palatine Greater palatine nerve and vessels Lesser palatine foramen Palatine Lesser palatine nerve and vessels Pterygoid canal Sphenoid pterygoid nerve and vessels Carotid canal Temporal Internal carotid artery and nerve plexus Stylomastoid foramen Temporal Facial Nerve [VII]
Landmarks of the Skull:
- Bregma: intersection of coronal and sagittal sutures
- Lambda: intersection between lambdoid and sagittal sutures
- Glabella: depression of frontal bone between the superciliary arches
- Nasion: articulation of nasal and frontal bones - Pterion: junction of the frontal, parietal, temporal, and sphenoid bones. This area is of great relevance in skull fractures because the bone in this region is thin and overlies the anterior division of the middle meningeal artery
Cranial Cavity:
Roof of the Cranial Cavity: the calvaria
- Consists of the frontal, parietal, and occipital bones
- Contains sutures between bones:
o Coronal suture: between frontal and parietal bones
o Sagittal suture: between paired parietal bones
o Lambdoid suture: between parietal and occipital bones, may contain sutural (wormian) bones
- Frontal Crest: midline ridge of bone on the frontal bone acts as attachment point for falx cerebri (dura mater that separates the two cerebral hemispheres)
- Groove for Superior Sagittal Sinus
- Grooves for Meningeal vessels
- Granular Foveolae: mark locations of arachnoid granulations (involved in CSF reabsorption)
Floor of the Cranial Cavity:
- Anterior cranial fossa: parts of frontal, ethmoid, and sphenoid bones
o Filled by frontal lobes of cerebral hemispheres
o Crista galli: located on the ethmoid, acts as another point of attachment for the falx cerebri
o Cribiform Plate: located on ethmoid, allows passage of small olfactory nerves
o Anterior Clinoid Process: end of lesser wing of scaphoid that serves as attachment for the Tentorium Cerebelli (dura separating the cerebral hemispheres from the cerebellum)
o Chiasmatic Sulcus serves as border between anterior and middle fossae
- Middle cranial fossa: parts of sphenoid and temporal bones
o Sella turcica: body of sphenoid, consisting of hypophysial fossa which contains the pituitary gland
o Posterior Clinoid Process: located on lateral end of dorsum sellae (on sella turcica) and serve as another attachment point for the tentorium cerebelli
o Trigeminal Impression: located on the temporal bone, the location of the sensory ganglion of the Trigeminal Nerve [V]
o Arcuate Eminence: rounded protrusion of temporal bone produced by the underlying anterior semicircular canal of the inner ear
o Tegmen Tympani: part of temporal bone that marks the roof of the middle ear
- Posterior cranial fossa: mostly temporal and occipital bones with small contributions from the sphenoid and parietal bones.
o The largest and deepest of the cranial fossa
o Contains the brainstem and cerebellum
o Clivus: slope of sphenoid and occipital bones that extends upward from the foramen magnum
o Groove for Inferior Petrosal Sinus: between basal part of occipital bone and petrous part of temporal bone
o Groove for Sigmoid Sinus
o Jugular Tubercle: just superior to jugular foramen
o Internal Occipital Crest and Protuberance and Groove for Transverse Sinus
Internal Foramina:
Foramen Bone Contents Foramen cecum Frontal Emissary veins Olfactory foramina Ethmoid Olfactory nerves [I] Optic canal Sphenoid Optic Nerve [II] and ophthalmic artery Superior orbital Sphenoid Oculomotor Nerve [III], Trochlear Nerve [IV], Ophthalmic nerve fissure [V1], Abducent Nerve [VI], and ophthalmic veins Foramen rotundum Sphenoid Maxillary nerve [V2] Mandibular nerve [V3], lesser petrosal nerve (carrying fibers of Foramen ovale Sphenoid tympanic plexus from Glossopharyngeal Nerve [IX]), accessory middle Meningeal artery Foramen spinosum Sphenoid Middle Meningeal artery and associated veins Hiatus for greater Temporal Greater petrosal nerve (branch of Facial Nerve [VII]) petrosal nerve Hiatus for lesser Temporal Lesser petrosal nerve (carrying fibers of tympanic plexus from petrosal nerve Glossopharyngeal Nerve [IX]) Foramen lacerum Sphenoid Cartilage Foramen magnum Occipital Spinal cord, meninges, vertebral arteries, and the spinal roots of the Accessory Nerve [XI] Internal acoustic Temporal Facial Nerve [VII], Vestibulocochlear Nerve [VIII], and the meatus labyrinthine artery Between Sigmoid sinus forming the Internal jugular vein, Jugular foramen Temporal and Glossopharyngeal Nerve [IX], Vagus Nerve [X], and the Occipital Accessory Nerve [XI] Hypoglossal canal Occipital Hypoglossal Nerve [XII] leaves and Meningeal branch of ascending pharyngeal artery (external carotid) enters Condylar canal Occipital Emissary vein