58 BASE OF THE SKULL. 



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 

 (foramen 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 max- 

 illary nerve ; foramen ovate, for the inferior maxillary nerve, arteria 

 meningea parva, and nervus petrosus superficialis minor ; foramen 

 spinosum, for the arteria meningea magna ; 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 Fal/opii, 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 depression for the Casserian ganglion. Farther 

 outwards is the eminence which marks the position of the perpen- 

 dicular semicircular canal. Proceeding from the foramen spinosum 

 are two grooves which mark 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 by the poste- 

 rior clinoid processes, and along its posterior circumference by the 

 groove for the lateral sinuses, and gives support to the pons Varolii, 

 medulla oblongata, and cerebellum. In the centre of this fossa is 

 the foramen magnum bounded 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 con- 

 cave surface which supports the medulla oblongata and pons Va- 

 rolii, and on each side the following foramina from before back- 

 wards. The internal auditory foramen, for the auditory and facial 

 nerve and auditory artery ; behind, and external to this is a small 

 foramen leading into the aquceductus vestibuli ; and below it, partly 

 concealed by the edge of the petrous bone, the aqucsductus cochlece ; 

 next, a long fissure, the foramen lacerum posterius, or jugular fora- 

 men, giving passage to the commencement of the internal jugular 

 vein and the eighth pair of nerves. Converging towards this fora- 

 men from behind is the deep grove for the lateral sinus, and from 

 the front the groove for the inferior petrosal sinus. 



Behind the foramen magnum is a longitudinal ridge, which gives 

 attachment to the falx cerebelli, and divides the two inferior fossae of 

 the occipital bone ; and above the ridge is the elevation correspond- 

 ing with the tubercle of the occipital bone and the transverse groove 

 lodging the lateral sinus. 



