Cranial Cavity and Skull Anatomy

• The cranial cavity houses the brain, meninges, cranial nerves, arteries, veins, and venous sinuses

Vault of the Skull

• The internal surface displays coronal, sagittal, and lambdoid sutures
• The midline features a shallow sagittalgroove which lodges the superior sagittal sinus
• Granular pits are small pits that lodge lateral lacunae and arachnoid granulations
• Narrow grooves accommodate anterior and posterior divisions of the middle meningeal vessels

Base of the Skull

• The interior is divided into anterior, middle, and posterior cranial fossae
• The lesser wing of the sphenoid separates the anterior and middle cranial fossae
• The petrous part of the temporal bone separates the middle and posterior cranial fossae

Anterior Cranial Fossa

• The anterior cranial fossa lodges the frontal lobes of the cerebral hemispheres
• Anteriorly bounded by the inner surface of the frontal bone
• The midline has a frontal crest for the attachment of the falx cerebri
• The posterior boundary is the lesser wing of the sphenoid
• The medial end of the lesser wing forms the anterior clinoid process, which attaches to the tentorium cerebelli
• The groove for the optic chiasma limits the median part of the anterior cranial fossa posteriorly
• The floor is formed by the ridged orbital plates of the frontal bone laterally and the cribriform plate of the ethmoid medially
• The crista galli is an upward projection of the ethmoid bone for the attachment of the falx cerebri
• The upper surface of the cribriform plate supports the olfactory bulbs
• Small perforations in the cribriform plate are for the olfactory nerves

Middle Cranial Fossa

• The middle cranial fossa has a small median part and expanded lateral parts
• The body of the sphenoid forms the median raised part
• The lateral parts form concavities lodging the temporal lobes of the cerebral hemispheres
• The fossa is bounded anteriorly by the lesser wings of the sphenoid
• The posterior boundary is the superior borders of the petrous parts of the temporal bones
• Squamous parts of the temporal bones, greater wings of the sphenoid, and parietal bones lie laterally
• The floor of each lateral part is formed by the greater wing of the sphenoid and the squamous and petrous parts of the temporal bone
• The sphenoid bone resembles a bat with a centrally placed body and outstretched greater and lesser wings
• The sphenoid air sinuses are lined with mucous membrane, communicate with the nasal cavity, and serve as voice resonators
• The optic canal transmits the optic nerve and ophthalmic artery
• The superior orbital fissure transmits lacrimal, frontal, and nasociliary branches of the ophthalmic division of the trigeminal nerve, trochlear, oculomotor, and abducent nerves, along with the superior ophthalmic vein
• The sphenoparietal venous sinus drains into the cavernous sinus
• Foramen rotundum transmits the maxillary nerve from the trigeminal ganglion to the pterygopalatine fossa
• The foramen ovale transmits the large sensory root and small motor root of the mandibular nerve to the infratemporal fossa, along with the lesser petrosal nerve
• The foramen spinosum transmits the middle meningeal artery from the infratemporal fossa into the cranial cavity
• The foramen lacerum is between the apex of the petrous part of the temporal bone, sphenoid bone, and occipital bone
• The inferior opening of the foramen lacerum is filled with cartilage and fibrous tissue, with small blood vessels passing through
• The carotid canal opens into the side of the foramen lacerum
• The internal carotid artery enters through the carotid canal
• An impression for the trigeminal ganglion is lateral to the foramen lacerum
• Grooves on the anterior surface of the petrous bone are for nerves
• The largest medial groove is for the greater petrosal nerve, a branch of the facial nerve
• The smaller lateral groove is for the lesser petrosal nerve, a branch of the tympanic plexus
• The greater petrosal nerve joins the deep petrosal nerve (sympathetic fibers from around the internal carotid artery) to form the nerve of the pterygoid canal
• The lesser petrosal nerve passes forward to the foramen ovale
• The median part of the middle cranial fossa is formed by the body of the sphenoid bone
• The sulcus chiasmatis is in front and related to the optic chiasma
• The tuberculum sellae is posterior to the sulcus
• The sella turcica is a deep depression behind the elevation, lodging the pituitary gland
• The dorsum sellae, a square plate of bone, bounds the sella turcica posteriorly
• Posterior clinoid processes are tubercles on the superior angles of the dorsum sellae that attach to the tentorium cerebelli
• The cavernous sinus carries cranial nerves III, IV, and the ophthalmic and maxillary divisions of V in its lateral wall
• The internal carotid artery and cranial nerve VI pass through the sinus

Posterior Cranial Fossa

• The posterior cranial fossa is deep and lodges the cerebellum, pons, and medulla oblongata

• The superior border of the petrous part of the temporal bone bounds it anteriorly

• The internal surface of the squamous part of the occipital bone bounds it posteriorly

• The floor is formed by the basilar, condylar, and squamous parts of the occipital bone and the mastoid part of the temporal bone

• The roof is formed by the tentorium cerebelli

• The foramen magnum transmits the medulla oblongata, meninges, spinal accessory nerves, and vertebral arteries

• The hypoglossal canal transmits the hypoglossal nerve

• The jugular foramen transmits the inferior petrosal sinus; cranial nerves IX, X, and XI; and the sigmoid sinus

• The internal acoustic meatus transmits the vestibulocochlear nerve and the facial nerve

• The internal occipital crest attaches to the falx cerebella over the occipital sinus

• A wide groove for the transverse sinus sweeps to the postero-inferior angle of the parietal bone

• The transverse sinus becomes the sigmoid sinus on the mastoid part of the temporal bone

• The superior petrosal sinus drains into the sigmoid sinus

• The sigmoid sinus grooves the petrous bone and mastoid part of the temporal bone as it descends to the jugular foramen

Major Foramina and Fissures: Superior View of the Cranial Base

• Cribriform plate: Ethmoid; Olfactory nerves from the olfactory bulb
• Foramen cecum: Ethmoid bones; Emissary vein from nasal cavity to the superior sagittal sinus
• Anterior ethmoid foramen: Between the frontal and ethmoid bones; Anterior ethmoid nerve and vessels
• Posterior ethmoid foramen: Between the frontal and ethmoid bones; Posterior ethmoid nerve and vessels
• Optic canal: Sphenoid; Optic nerve and ophthalmic artery
• Superior orbital fissure: Between the greater and lesser wings of the sphenoid; Nasociliary, frontal, and lacrimal branches of the ophthalmic division of the trigeminal nerve, oculomotor nerve, trochlear nerve, abducens nerve, superior ophthalmic vein
• Foramen rotundum: Sphenoid; Maxillary division of the trigeminal nerve
• Foramen ovale: Sphenoid; Mandibular division of the trigeminal nerve, accessory meningeal artery, lesser petrosal nerve, emissary vein
• Foramen spinosum: Sphenoid; Middle meningeal vessels and meningeal branch of the mandibular division of the trigeminal nerve
• Foramen lacerum: Articulation of the sphenoid, temporal, and occipital bones; Filled with fibrocartilage, may have openings for the pterygoid and carotid canals
• Carotid canal: Articulation of the sphenoid, temporal, and occipital bones; Internal carotid artery and internal carotid nerve plexus (sympathetics)
• Hiatus for the lesser petrosal nerve: Temporal; Lesser petrosal nerve
• Hiatus for the greater petrosal nerve: Temporal; Greater petrosal nerve
• Internal acoustic meatus: Temporal; Facial nerve and vestibulocochlear nerve
• Jugular foramen: Temporal and occipital; Glossopharyngeal nerve, vagus nerve, spinal accessory nerve, inferior petrosal sinus, sigmoid sinus
• Hypoglossal canal: Occipital; Hypoglossal nerve
• Foramen magnum: Occipital; Medulla oblongata, vertebral arteries, spinal roots of the spinal accessory nerve

Inferior View of the Cranial Base

• Incisive foramen: Maxilla; Nasopalatine nerve and sphenopalatine artery
• Greater palatine foramen: Palatine bone; Greater palatine nerve and vessels
• Lesser palatine foramina: Palatine bone; Lesser palatine nerve and vessels
• Foramen ovale: Sphenoid bone; Mandibular division of the trigeminal nerve, accessory meningeal artery, and lesser petrosal nerve
• Foramen spinosum: Sphenoid bone; Middle meningeal vessels and meningeal branch of the mandibular division of the trigeminal nerve
• Foramen lacerum: Between sphenoid, temporal, and occipital bones; Filled with fibrocartilage with the carotid canal inside
• Carotid canal: Temporal bone; Internal carotid artery and the internal carotid nerve plexus
• Jugular foramen: Temporal and occipital bone; Glossopharyngeal, vagus and spinal accessory nerves ,inferior petrosal and sigmoid sinuses
• Stylomastoid foramen: Temporal bone; Facial nerve and stylomastoid artery
• Hypoglossal canal: Occipital bone; Hypoglossal nerve
• Foramen magnum: Occipital bone; Medulla oblongata, vertebral arteries, and spinal root of accessory nerve

Anterior View of the Cranial Openings

• Supraorbital foramen-Frontal bone-Supraorbital nerve and vessels
• Optic canal-Sphenoid bone-Optic nerve and ophthalmic artery
• Superior orbital fissure-Greater and lesser wing of sphenoid-Nasociliary, frontal, and lacrimal branches of the ophthalmic division of the trigeminal nerve, oculomotor, trochlear, abducens nerves and superior ophthalmic vein
• Inferior orbital fissure-Greater wing of sphenoid and maxilla and orbital portion of palatine bones-Maxillary division of trigeminal nerve, infraorbital vessels, and inferior ophthalmic vein
• Anterior ethmoid foramen-Frontal and ethmoid bones-Anterior ethmoid nerve and vessels
• Posterior ethmoid foramen-Frontal and ethmoid bones-Posterior ethmoid nerve and vessels
• Zygomatico facial foramen-Zygomatic bone-Zygomatico facial nerve and vessels
• Infraorbital foramen-Maxilla bone-Infraorbital nerve and vessels
• Mental foramen-Mandible bone-Mental nerve and vessels