BASE OF THE SKULL. 57 



boundary. It supports the anterior lobes of the cerebrum. In the 

 middle line of this fossa, at its anterior part, is the crista galli, im- 

 mediately in front of this process, the foramen caecum, and on each 

 side the cribriform plate, with its foramina, for the transmission of the 

 filaments of the olfactory and nasal branch of the ophthalmic nerve. 

 Farther back in the middle line is the processus olivaris, and on the 

 sides of this process the optic foramina, anterior and middle clinoid 

 processes, and vertical grooves for the internal carotid arteries. 



The middle fossa of the base, deeper than the preceding, is bounded 

 in front by the lesser wing of the sphenoid ; behind, by the petrous 

 portion of the temporal bone ; and is divided into two lateral parts by 

 the sella turcica. It is formed by the posterior part of the body, 

 great ala, and spinous process of the sphenoid, and by the petrous and 

 squamous portion of the temporal bones. In the centre of this fossa 

 is the sella turcica which lodges the pituitary gland, bounded in 

 front by the anterior and middle and behind by the posterior clinoid 

 processes. On each side of the sella turcica is the carotid groove 

 for the internal carotid artery, the cavernous plexus of nerves, the 

 cavernous sinus, and the orbital nerves, and a little farther outwards 

 the following foramina from before backwards, sphenoidal fissure (fora- 

 men lacerum anterius) for the transmission of the third, fourth, three 

 branches of the ophthalmic division of the fifth, and the sixth nerve, 

 and ophthalmic vein ; foramen rotundum, for the superior maxillary 

 nerve ; foramen ovale, for the inferior maxillary nerve, arteria menin- 

 gea parva, and nervus petrosus superficial minor ; foramen spinosum, 

 for the arteria meningea media ; foramen lacerum basis cranii, which 

 gives passage to the internal carotid artery, carotid plexus, and 

 petrosal branch of the Vidian nerve. On the anterior surface of the 

 petrous portion of the temporal bone is a groove, leading to a fissured 

 opening, the hiatus Fallopii, for the petrosal branch of the Vidian 

 nerve ; and immediately beneath this a smaller foramen, for the 

 nervus petrosus superficialis minor. Towards the apex of this portion 

 of bone is the notch for the fifth nerve, and below it a slight depres- 

 sion for the Casserian ganglion. Farther outwards is the eminence 

 which marks the position of the perpendicular semi-circular canal. 

 Proceeding from the foramen spinosum are t^vo grooves which indicate 

 the course of the trunks 'of the arteria meningea media. The whole 

 fossa lodges the middle lobes of the cerebrum. 



The posterior fossa, larger than the other two, is formed by the 

 occipital bone, by the petrous and mastoid portion of the temporals, 

 and by a small part of the sphenoid and parietals. It is bounded in 

 front by the upper border of the petrous portion and dorsum ephippii, 

 and along its posterior circumference by the groove for the lateral 

 sinuses ; it gives support to the pons Varolii, medulla oblongata and 

 cerebellum. In the centre of this fossa is the foramen magnum bound- 

 ed on each side by a rough tubercle, which gives attachment to the 

 odontoid ligament, and by the anterior condyloid foramen. In front 

 of the foramen magnum is the concave surface (clivus Blumenbachii) 



