THE SKELETON IN REPTILES. THE RIBS. 



285 



THE RIBS. 



Ribs are always present, and may be attached to any of the 

 precaudal vertebrae. In most reptiles the posterior cervical 

 vertebrae bear ribs, while the atlas and axis are ribless ; in 

 Crocodiles and Geckos, however, ribs are borne even by the 

 atlas and axis. On the other hand, in the Chelonia none of 



FIG. 53. HYOIDS OF AN ALLIGATOR (Caiman latirostris) (TO THE LEFT) 

 AND OF A GREEN TURTLE (Chelone midas) (TO THE RIGHT) x f. 

 (Brit. Mus.) 



The cartilaginous portions are dotted. 



1. basilingual plate or body of 3. first branchial arch (anterior 



the hyoid. cornu). 



2. hyoid arch. 4. second branchial arch (pos- 



terior cornu.) 



the cervical vertebrae bear obvious ribs. In the following 

 groups the thoracic ribs have both capitula and tubercula 

 Theromorpha, Ichthyosauria, Crocodilia, Dinosauria, Ptero- 

 sauria. In the other groups each rib articulates by a single 



