114 ALUS. [Vol. XVIII. 



line. The middle portions of the webs, especially those portions 

 that lie immediately in front of the spines, are not so united, being 

 always separated by a wide open space. The spine-like portions 

 of the arches of opposite sides are not connected with each other 

 at the level of the dorsal surface of the spinal canal. Somewhat 

 above that canal they fuse to form a single median spine, which 

 extends upward and backward, curving slightly, and ending in a 

 sharp point. The spines incline backward, progressively more 

 and more strongly from the first to the sixth vertebra. 



Posterior to the base of the spine of each vertebra the webbed 

 part of the arch is' pierced by one or two foramina, which transmit 

 the roots of the associated' spinal nerve. These foramina, on the 

 posterior vertebrae examined, lie immediately posterior to the base 

 of the spine of their vertebrae, while on the anterior vertebrae, ex- 

 cepting only the first vertebra, they lie slightly distant from it. 

 The ventral foramen on the first vertebra lies in the base of 

 the spine, itself, that base on this vertebra spreading much 

 more than on the posterior ones. Ordinarily there are two 

 foramina in each vertebra, one for the dorsal root of the spinal 

 nerve that innervates the muscle segment that lies between the 

 vertebra in question and the next posterior one, and the other 

 for the ventral root of the same nerve. 



On the anterior edge of the first vertebra there is a large, strong 

 process, directed forward, or forward and slightly upward. It 

 arises from that part of the edge of the vertebra that lies between 

 the mid-lateral line of the body of the vertebra and the lateral edge 

 of the spinal canal. Its mesial edge is strongly bevelled, a broad 

 surface being formed which looks mesially, forward and slightly 

 upward. It is lined with what seems to be fibro-cartilage and it 

 articulates with the long, oval articular surface on the hind end 

 of the occipitale laterale. On each of the other vertebrae a cor- 

 responding process is also found, but it is less strongly developed 

 and lies more dorsally on its vertebra. It overlaps externally the 

 dorso-lateral surface of the next preceding vertebra, and articu- 

 lates both with that surface and with the dorsal edge of a poste- 

 rior process of the same vertebra. This latter process arises from 

 the hind edge of the vertebra concerned, is a small, somewhat 

 pointed process directed backward and laterally, and fits into or 



