Back to NeuroanatomyThe internal surface of the base of the skull consists of three cranial fossae, the anterior, middle, and posterior. They increase in size and depth from before backward. The anterior and middle fossae are separated by the lesser wing of sphenoid bone, and the middle and posterior fossae are separated by petrous part of temporal bone
The anterior cranial fossa is adapted for reception of the frontal lobes of the brain, and is formed by portions of frontal, ethmoid and sphenoid bones. Anteriorly and laterally it is limited by frontal bone, and posteriorly by the posterior border of the lesser wings of the sphenoid and the anterior margin of the prechiasmatic sulcus ( or chiasmatic groove ). The crista galli, a midline process of the ethmoid bone, gives attachment to the anterior end of the falx cerebri. On each side of the crista galli are the grooved cribiform plates of the ethmoid, providing numerous orifices for the delicate olfactory nerves from the nasal mucosa to synapse in the olfactory bulbs. The floor of this fossa, posterior to the ethmoid and frontal bones, is formed by the anterior part of the sphenoid bone, the jugum sphenoidale, and on each side, by the lesser wings of this bone.
The middle cranial fossa is composed of the body and great wings of the sphenoid, the squamous and petrous parts of the temporal bones and the frontal angles of the parietal bones. This fossa contains laterally the temporal lobes of the brain. The body of the sphenoid bone contains in this fossa the prechiasmatic sulcus (which contains the optic chiasma ) and the sella turcica ( it resembles a premedieval turkish saddle ), composed by the tuberculum sellae, hypophyseal fossa, posterior clinoid process and the dorsum sellae. The pituitary gland is within the hypophyseal fossa. The middle cranial fossa is limited posteriorly by the superior angle of the petrous portion of the temporal bone and the dorsum sellae centrally. From defore backward in the sphenoid bone is the superior orbital fissure, foramen rotundum, foramen ovale and foramen spinosum. Medially, between the sphenoid and temporal bones is the foramen lacerum. In the temporal bone are the hiatus of canal of lesser and of greater petrosal nerves. On the anterior surface of the petrous portion of the temporal bone is the trigeminal impression which lodges the trigeminal ganglion ( semilunar or gasserian ) of the fifth nerve.
Superior orbital fissure
1- Oculomotor ( III ) nerve;
2- Trochlear ( IV ) nerve;
3- Ophthalmic ( V.1 ) nerve;
4- Abducens ( VI ) nerve;
5- Superior ophthalmic vein;
Foramen rotundum
1- Maxillary ( V.2 ) nerve;
Foramen ovale
1- Mandibular ( V.3 ) nerve;
2- Accessory meningeal artery;
3- Lesser petrosal nerve ( occasionally );
Foramen spinosum
1- Middle meningeal artery and vein;
2- Meningeal branch of mandibular nerve;
Foramen lacerum
1- Internal carotid internal;
2- Internal carotid nervous plexus.
The posterior cranial fossa, the deepest of the fossae is bounded anteriorly by the dorsum sellae of the sphenoid bone and the basilar part of the occipital bone; laterally by the petrous and mastoid parts of the temporal bones, the mastoid angles of the parietal bones, and the lateral parts of the occipital bone; posteriorly, by the squama of the occipital bone below the sulci for the transverse sinuses and the internal occipital protuberance. The fossa contains the cerebellum, pons, and medulla oblongata. There are four important foramina, the internal acoustic meatus ( in the petrous part of the temporal bone ), the jugular foramen ( between the sphenoid and occipital bones ), the hipoglossal canal (in the occipital bone ), and the foramen magnum ( a large median opening in the floor of the fossa, where the medulla oblongata is continuous with the spinal cord ).
Internal acoustic meatus
1- Facial ( VII ) nerve;
2- Vestibulocochlear ( VIII ) nerve;
3- Labyrinthine artery;
Jugular foramen
1- Inferior petrosal sinus;
2- Glossopharyngeal ( IX ) nerve;
3- Vagus ( X ) nerve;
4- Accessory ( XI ) nerve;
5- Sigmoid sinus;
Hypoglossal canal
1- Hypoglossal ( XII ) nerve;
Foramen magnum
1- Medulla Oblongata;
2- Meninges;
3- Vertebral arteries;
4- Spinal roots of accessory nerves.
Back to Neuroanatomy
Back to Basic Sciences
Back to MEDSTUDENTS' HOMEPAGE