THE CEOCODILIA. 251 



The majority of the pre-cretaceous Crocodilia have the cor- 

 responding vertebra amphicoelous, the concavities of the 

 centra being very shallow. One gemis, Streptospondylus, 

 which is perhaps Crocodilian, has the anterior vertebrae 

 opisthocoelous. It is characteristic of the Crocodilia, that 

 the centra of the vertebrae are united by fibro-cartilages, 

 and that the neurocentral sutures persist for a long time, 

 or throughout life. 



The atlas is composed of foiu- pieces, an upper median 

 piece — which is sometimes divided into two, and is developed 

 in membrane apart from the rest — heing added to the 

 three pieces found in Lacertilia and Chelonia. A large 

 odontoid bone is closely united to, but not ankylosed with, 

 the anterior flat face of the second vertebra. A pair of 

 elongated, single-headed ribs are attached to the inferior 

 piece of the atlas, and another similar pair to the os odon- 

 toidum and to the second vertebra, by distinct capitular 

 and tubercular processes. The other cervical vertebra all 

 possess ribs with distinct and long capitula and tuberciila — 

 the latter attached above the neurocentral suture to the 

 neural arch, the former to the centrum below the neuro- 

 central suture. The body of each cervical rib, after the 

 second, and as far as the seventh or eighth, is short, and 

 prolonged in front of, as well as behind, the junction of the 

 capitulum with the tuberculum ; and the several ribs lie 

 nearly parallel with the vertebral column, and overlap one 

 another. The ribs of the eighth and ninth cervical vertebrae 

 are longer, and take on more the character of the dorsal ribs, 

 the ninth having a terminal cartilage. 



The points to which the capitula and tubercula of the 

 ribs are attached are raised into tubercles ; and, by degrees, 

 these become elongated into distinct capitular and tuber- 

 cular processes, between which, in the third to the ninth 

 vertebrae, the neurocentral suture passes. But in the tenth 

 and in the eleventh vertebrae, the capitular process, which 

 lies nearer the neurocentral suture in the posterior than 

 in the anterior ceiwical vertebrae, rises upon the body of 

 the vertebra to the level of the neurocentral suture, by 



