Interior of skull

The Cranial FossaeCranial fossa – curving

depression of the cranial floor

Anterior cranial fossa formed by: frontal bone, ethmoid, lesser wing of the sphenoid;

cradles the frontal lobes of the cerebral hemispheres

Middle cranial fossa is formed by:sphenoid, temporal, parietal bones; cradles the temporal lobes of the cerebral hemispheres, the diencephalon, and mesencephalon

Posterior cranial fossa is formed primarily by:occipital bone, with contributions from the temporal and parietal bones- suports the occipital lobes of the crebral hemispheres, the crebellum, and the pons and medulla oblongata (brain stem)

The Cranial Fossae

Interior of the Cranial CavityCranial cavity: occupied by the brain Calvaria (skull cap): upper dome-like portion of skull

Floor divided into anterior, middle, and posterior fossae

Crista galli: prominent ridge in center of anterior fossa. Point of attachment for the dura mater (one of the meninges)

Olfactory fossae lateral to crista galli. Olfactory bulb within Cribriform plate of the ethmoid forms floor of olfactory fossae Olfactory nerves pass through the foramina of the cribriform plate

Sella turcica: part of sphenoid bone that houses the pituitary gland Foramen magnum: opening where brain attaches to spinal cord

Anterior cranial Fossa

The floor of the anterior fossa is formed by:

Orbital plates of the frontal,

Cribriform plate of the ethmoid small wings and front part of the body of the sphenoid

It is limited behind by the posterior borders of the small wings of the sphenoid and by the anterior margin of the chiasmatic groove.

It is traversed by the frontoethmoidal suture

sphenoethmoidal suture sphenofrontal sutures.

The central portion corresponds with the roof of the nasal cavity, and is markedly depressed on either side of the crista galli.

It presents, in and near the median line, from before backward, the commencement of the frontal crest for the attachment of the falx cerebri

Foramen cecum, The frontal crest of the frontal bone ends below in a small notch which is converted into a foramen, by articulation with the ethmoid

It transmits a vein from the nose to the superior sagittal sinus

Crista galli, ridge behind the foramen cecum, the free margin of which affords attachment to the falx cerebri

Olfactory groove on either side of the crista galli, formed by the cribriform plate,

Supports the olfactory bulb and presents foramina for the transmission of the olfactory nerves,

In front a slit-like opening for the nasociliary nerve.

Anterior ethmoidal foramen

situated about the middle of the lateral margin of the olfactory groove,

Transmits the anterior ethmoidal vessels and the anterior ethmoidal nerve

Posterior ethmoidal foramen Opens at the back part of this margin under cover of the projecting lamina of the sphenoid

transmits the posterior ethmoidal vessels and nerve

Middle cranial Fossa Deeper than the preceding, is narrow in the middle, and wide at the sides of the skull.

It is bounded in front by the posterior margins of the small wings of the sphenoid, the anterior clinoid processes, ridge forming the anterior margin of the chiasmatic groove;

behind, by the superior angles of the petrous portions of the temporals and the dorsum sella

laterally by the temporal squama, sphenoidal angles of the parietals, and great wings of the sphenoid.

It is

traversed by the squamosal, sphenoparietal, sphenosquamosal, sphenopetrosal sutures.

Chiasmatic groove The superior surface of the body of the sphenoid bone is bounded behind by a ridge, which forms the anterior border of a narrow, transverse groove, the chiasmatic groove (optic groove)

Tuberculum sella In the sphenoid bone, behind the chiasmatic groove is an elevation, the tuberculum sellae.

sella turcica Deep depression Behind the tuberculum sella Contains the fossa hypophyseos, which lodges the hypophysis, and presents on its anterior wall the middle clinoid processes

Bounded posteriorly by a quadrilateral plate of bone, the dorsum sella, upper angles are surmounted by the posterior clinoid processes

Gives attachment to the tentorium cerebelli, and below each is a notch for the abducent nerve

On either side of the sella turcica is the carotid groove

Optic foramen The optic foramen is the opening to the optic canal.

Transmits the optic nerve and ophthalmic artery (with accompanying

sympathetic nerve fibres) into the orbital cavity.

Behind the optic foramen the anterior clinoid process is directed backward and medialward and gives attachment to the tentorium cerebelli

Superior orbital fissure

Bounded Above by the small wing

Below, by the great wing,

Medially, by the body of the sphenoid

Laterally by the orbital plate of the frontal bone.

Transmits to the orbital cavity

oculomotor, trochlear, ophthalmic division of the trigeminal, abducent nerves, some filaments from the cavernous plexus of the sympathetic, the orbital branch of the middle meningeal artery;

From the orbital cavity Recurrent branch from the lacrimal artery to the dura mater, and the ophthalmic veins

Foramen rotundum

Behind the medial end of the superior orbital fissure

Provides passage for the maxillary nerve.

Foramen ovale At base of lateral pterygoid plate

Through which passes mandibular nerve, accessory meningeal artery, & lesser petrosal nerve

Foramen spinosum

Posterior & somewhat lateral to foramen ovale

Transmits middle meningeal vessels & small meningeal branch of mandibular

Foramen lacerum At base of medial pterygoid plate in dried skull Not complete foramen in intact body, because its inferior part is covered over by fibrocartilaginous plate, across superior (inner or cerebral) surface of which passes internal carotid artery.

Carotid canal Inferior surface of petrous temporal bone is pierced by round opening.

Internal carotid artery, coursing within canal, immediately takes right angle turn to reach side of foramen lacerum.

Hiatus for greater petrosal nerve (or hiatus of the facial canal )

A shallow groove, sometimes double, leading lateralward and backward to an oblique opening for the passage of the

greater superficial petrosal nerve petrosal branch of the middle meningeal artery.

Facial canal (also known as Fallopian Canal) is a Z-shaped canal running through the temporal bone from the internal acoustic meatus to the stylomastoid foramen.

In humans it is approximately 3 centimeters long, which makes it the longest human osseous canal of a nerve

It is located within the middle ear region, according to its shape it is divided into three main segments: the labyrinthine, the tympanic, and the mastoidal segment.

Posterior cranial Fossa The posterior fossa is the largest and deepest of the three.

It is formed by

Dorsum sella and clivus of the sphenoid Occipital Petrous and mastoid portions of the temporals Mastoid angles of the parietal bones

Crossed by the occipitomastoid suture parietomastoid sutures

lodges the cerebellum, pons, and medulla oblongata.

Foramen magnum Posterior to basilar portion of occipital bone

Transmits- Medulla oblongata & its

membranes- Accessory nerves- Vertebral arteries- Anterior & posterior

spinal arteries- Ligaments connecting

occipital bone with axis

Hypoglossal canal

Courses forward & laterally from inner aspect of occipital bone within cranium just

above foramen magnum to opening that perforates occipital bone externally at lateral part of base of occipital condyle

Transmits hypoglossal nerve & a branch of posterior meningeal artery

Jugular foramen is situated between the lateral part of the occipital and the petrous part of the temporal

Anterior compartment – inferior petrosal sinus

Intermediate – glossopharyngeal, vagus, & accessory nerves Posterior – sigmoid sinus which leads to internal jugular vein, & some meningeal branches from occipital & ascending pharyngeal arteries

Internal auditory meatus (also internal acoustic meatus,) is a canal in the petrous part of the temporal bone of the skull that carries nerves from inside the cranium towards the middle and inner ear compartments

Namely cranial nerve VII and cranial nerve VIII.