Bones of the Cranial Cavity

Nyra E. Montera Nov. 11, 2008

• Important Landmarks on the Skull

• Fossae and Foramen at the base of the skull

=> external aspect

=> internal aspect

Landmark Shape and Location

Pterion (G. wing)

Junction of the greater wing of the sphenoid, squamous temporal, frontal, and parietal bones; overlies course of anterior division of middle meningeal artery

Lambda (G. the letter L)Point on calvaria at junction of lambdoid and sagittal sutures

Bregma (G. forepart of the head)Point on calvaria at junction of coronal and sagittal sutures

Vertex (L. whirl or whorl)Superior point of neurocranium in the midline with skull oriented in anatomical (orbitorneal or Frankport) plane

Asterion (G. asterios, starry)Star-shaped; located at junction of three sutures; parietomastoid, occipitomastoid, and lambdoid

Glabella (L. smooth, hairless)Smooth prominence, most marked in males, on the frontal bone superior to the root of nose; most anterior projecting part of forehead

Nasion (L. nose)Point on skull where frontonasal and internasal sutures meet

Inion (G. back of head)Most prominent point of external occipital protuberance

glabella

External Aspect of the Base of the Skull

Internal Aspect of the Base of the Skull

Anterior cranial fossa

Posterior cranial fossa

Middle cranial fossa

the shallowest of the three fossae. formed by the

anteriorly: frontal bone

middle: the ethmoid bone,

posteriorly: the body and lesser wings of the sphenoid.

The greater part of this fossa is formed by the ridged orbital parts of the frontal bone which support the frontal lobes of the brain and form the roofs of the orbits

Anterior cranial fossa

Anterior Cranial Fossa Contents

Foramen cecumNasal emissary vein (1% of the population)

Foramina in cribriform plate

Axons of olfactory cells in olfactory epithelium that form olfactory nerves

Anterior and posterior ethmoidal foramina

Vessels and nerves with same names

Middle cranial fossa

butterfly-shapedPosteroinferior to the anterior cranial fossaThe bones forming the fossa are:

laterally: greater wings of the sphenoid bone

posteriorly: the petrous parts of the temporal bones

Supports the temporal lobes of the brain

Middle Cranial Fossa Contents

Optic canal Optic nerves (CN II) and ophthalmic arteries

Superior orbital fissures

Ophthalmic veins, ophthalmic nerve (CN V1),

CN III, IV, and VI, and sympathetic fibers

Foramen rotundum Maxillary nerve (CN V2)

Foramen ovaleMandibular nerve (CN V3) and accessory

meningeal artery

Foramen spinosumMiddle meningeal artery and vein and meningeal branch of CN V3

Foramen lacerumInternal carotid artery and its accompanying sympathetic and venous plexuses

Groove or hiatus of greater petrosal nerve

Greater petrosal nerve and petrosal branch of middle meningeal artery

Posterior cranial fossa

the largest and deepest of the three fossae

Lodges the cerebellum, pons and medulla oblongata

Anteriorly: it extends to the apex of the petrous temporal. Posteriorly: it is enclosed by the occipital bone. Laterally: portions of the squamous temporal and mastoid part of the temporal bone form its walls.

Posterior Cranial Fossa Contents

Foramen magnumMedulla and meninges, vertebral arteries, spinal roots of CN XI, dural veins, anterior and posterior spinal arteries

Jugular foramen

CNs IX, X, and XI, superior bulb of internal jugular vein, inferior petrosal and sigmoid sinuses, and meningeal branches of ascending pharyngeal and occipital arteries

Hypoglossal canal Hypoglossal nerve (CN XII)

Condylar canalEmissary vein that passes from sigmoid sinus to vertebral veins in neck

Mastoid foramenMastoid emissary vein from sigmoid sinus and meningeal branch of occipital artery

Special thanks to:

Dalley and Moore, clinically oriented anatomy 5th edition,(lippincott williams and wilkins, 2000), 841-847.