44 



THE OSTEOLOGY OF THE REPTILES 



The Skull of the Chelonia 



(Figs. 30-32) 

 The skull of the Testudinata or Chelonia is never elongate, though 

 relatively slender in some of the more predaceous kinds. It always 

 lacks the septomaxillae, postfrontals, supratemporals, dermosupra- 

 occipitals, tabulars, ectopterygoids, ethmoids, and the parietal fora- 

 men. The nasals are usually absent, and the lacrimals are present 



Fig. 32. Trionychoid skull: Platypeltis. Natural size. A, from above; 

 B, from below; C, atlas of same from the side. Note abnormal proatlas. 



only in some ancient forms. The prefrontals are large, meeting in 

 the middle line. The prevomers are single and sometimes obsolete; 

 they usually articulate above with the prefrontals. The para- 

 sphenoid has been lately recognized as a distinct bone in certain 

 forms. There is no postoptic, but its place is taken, except in Dermo- 

 chelys, by descending plates from the parietals to the pterygoids, 

 sometimes with an intercalated epipterygoid, which, however, is 

 usually absent. The quadrate may or may not reach the basisphe- 

 noid. The palatines often meet in the middle line between the pre- 



