BASE OF THE SKULL. 101 



anterius, or sphenoidal fissure, formed above by the lesser wing of the sphenoid ; 

 below, by the greater wing ; internally, by the body of the sphenoid ; and com- 

 pleted externally by the orbital plate of the frontal bone. It transmits the third, 

 fourth, the three branches of the ophthalmic division of the fifth, the sixth nerve, 

 and the ophthalmic vein. Behind the inner extremity of the sphenoidal fissure 

 is the foramen rotundnm, for the passage of the second division of the fifth or 

 superior maxillary nerve ; still more posteriorly is seen a small orifice, the foramen 

 Vesalii; this opening is situated between the foramen rotundum and foramen ovale, 

 a little internal to both ; it varies in size in different individuals, and transmits a small 

 vein. It opens below in the pterygoid fossa, just at the outer side of the scaphoid 

 depression. Behind and external to the latter opening is the foramen ovale, which 

 transmits the third division of the fifth or inferior maxillary nerve, the small 

 meningeal artery, and the small petrosal nerve. On the outer side of the foramen 

 ovale is the foramen spinosum, for the passage of the middle meningeal artery ; 

 and on the inner side of the foramen ovale, the foramen lacerum medium. The 

 lower part of this aperture is filled up with cartilage in the recent state. On the 

 anterior surface of the petrous portion of the temporal bone is seen, from without 

 inwards, the eminence caused by the projection of the superior semicircular canal, 

 and the groove leading to the hiatus Fallopii, for the transmission of the petrosal 

 branch of the' Vidian nerve; beneath it, the smaller groove, for the passage of the 

 smaller petrosal nerve ; and near the apex of the bone, the depression for the 

 Casserian ganglion, and the orifice of the carotid canal, for the passage of the 

 internal carotid artery and carotid plexus of nerves. 



The Posterior Fossa, deeply concave, is the largest of the three, and situated on 

 a lower level than either of the preceding. It is formed by the occipital, the 

 petrous and rnastoid portions of the temporal, and the posterior inferior angle of 

 the parietal bone ; is crossed by three sutures, the petro-occipital, masto-occipital, 

 and masto-parietal ; and lodges the cerebellum, pons Varolii, and medulla oblon- 

 gata. It is separated from the middle fossa in the median line by the basilar 

 suture, and on each side by the superior border of the petrous portion of the 

 temporal bone. This serves for the attachment of the tentorium cerebelli, is 

 grooved externally for the superior petrosal sinus, and at its inner extremity pre- 

 sents a notch, upon which rests the fifth nerve. Its circumference is bounded 

 posteriorly by the grooves for the lateral sinuses. In the centre of this fossa is 

 the foramen magnum, bounded on either side by a rough tubercle, which gives 

 attachment to the odontoid ligaments; and a little above these are seen the 

 internal openings of the anterior condyloid foramina. In front of the foramen 

 magnum is the basilar process, grooved for the support of the medulla oblongata 

 and pons Varolii, and articulating on each side with the petrous portion of the tem- 

 poral bone, forming the petro-occipital suture, the anterior half of which is grooved 

 for the inferior petrosal sinus, the posterior half being encroached upon by the 

 foramen lacerum posterius or jugular foramen. This foramen is partially subdi- 

 vided into two parts ; the posterior and larger division transmits the internal jugu- 

 lar vein, the anterior the eighth pair of nerves. Above the jugular foramen is the 

 internal auditory foramen, for the auditory and facial nerves and auditory artery; 

 behind and external to this is the slit-like opening leading into the aqua3ductus 

 vestibuli; whilst between the two latter, and near the superior border of the 

 petrous portion, is a small triangular depression, which lodges a process of 

 the dura mater, and occasionally transmits a small vein into the substance of the 

 bone. Behind the foramen magnum are the inferior occipital fossas, which lodge 

 the lateral lobes of the cerebellum, separated from one another by the internal 

 occipital crest, which serves for the attachment of the falx cerebelli, and lodges 

 the occipital sinuses. These fossae are surmounted, above, by the deep transverse 

 grooves for the lodgment of the lateral sinuses. These channels, in their passage 

 outwards, groove the occipital bone, the posterior inferior angle of the parietal, the 

 mastoid portion of the temporal, and the occipital just behind the jugular foramen, 

 at the back part of which they terminate. Where this sinus grooves the mastoid 



