288 ROBERT J. TERRY 



the cranium, forms the bottom of a deep sulcus whose sides are 

 constituted by the median walls of the cochleae. This sulcus is 

 occupied by no part of the brain, but is filled with a loose web of 

 mesenchymal tissue, in which the basilar artery and abducent 

 nerves run (fig. 22). Continuity between the cochlear promi- 

 nence and basal plate is brought about by means of a thin strip 

 of cartilage interrupted by the marginal foramina above men- 

 tioned. This strip is merely a septum between two oppositely 

 placed grooves, one outside, the other within the cranium, which, 

 in their semicircular courses, demarcate the limits between the 

 ear capsule and cranial floor (figs. 1, 2). These grooves ex- 

 tend anteriorly on the outside of the cranium beyond the con- 

 fines of the basal plate and include the carotid foramina; pos- 

 teriorly, both within and without the cranium, they have a some- 

 what lateral direction between the occipital division of the 

 floor and the otic capsule. Here are two large openings, the 

 jugular foramen, to be presently described, and the fissura 

 basicochlearis posterior (figs. 2, 12). The latter is sickle-shaped, 

 broad laterally where it approaches the jugular foramen, from 

 which it is separated by the commissura basi vestibularis. It 

 gives passage to no nerve or large vessel. 



The occipital portion of the basal plate forms the floor of the 

 occipital region of the cranium. It presents a slightly concave 

 intracranial surface and a convex face directed toward the naso- 

 pharyngeal duct ; at the sides it is continuous, at the level of the 

 hypoglossal canals and jugular foramina, with the lateral occipi- 

 tal walls. The caudal free margin is concave from side to side, 

 forming the ventral margin of the foramen occipitale magnum, 

 where on each side is the basal, smaller part of the occipital 

 condyle (fig. 19); between these is a shallow incisura occipitahs 

 anterior. 



The following observations were made on the position, rela- 

 tions and termination of the cranial portion of the notochord. 

 As shown in figures 14 and 19, this structure passes through the 

 middle of the body of the epistropheus, inclines ventrally on 

 entering the dens, and holds a position ventral of the middle of 

 the dens throughout the rest of its vertebral com-se. It leaves 



