22 2 THE OSTEOLOGY OF THE REPTn.ES 



3. ORDER TESTUDINATA OR CHELONIA 



Temporal region of skull usually exposed by the emargination 

 of the roof bones, the supratemporals, dermosupraoccipitals, and 

 tabulars absent. Eight cervicals. Ten dorsal vertebrae enclosed in. 

 a more or less complete carapace; an ossified plastron. A single 

 coracoid; pelvis with large openings. Phalangeal formula always 

 reduced. 



No order of reptiles is so unequivocally distinguished from all 

 others as the Chelonia, the turtles and tortoises. Jaws are always 

 [beaked], and except in Stegochelys of the Trias they are wholly 

 toothless; a short, broad body, a rather short skull, a flexible neck 

 of eight vertebrae, and an osseous carapace and plastron. 



In addition to the bones mentioned above, the postfrontals and ec- 

 toptery golds and usually the lacrimals are absent, the temporal region, 

 when roofed over, covered by the large postorbitals, jugals, squamo- 

 sals, and quadratojugals. The prevomers are united; there is no in- 

 terpterygoidal opening, and there may be an incipient secondary roof 

 to the palate. The prefrontals meet in the median line, the nasals 

 are often absent; the stapes is slender. The pectoral girdle is com- 

 posed of a furcate scapula and a single coracoid, usually without a 

 supracoracoid foramen. The carpus and tarsus are much modified, 

 and the phalangeal formula is always reduced, to 2, 3, 3, 3, 3 or 2, 2, 

 2, 2, 2, with the fifth toe usually still more so. Because of the inflex- 

 ible carapace the structure and posture of the limbs are much modi- 

 fied. The forearm is so twisted upon the humerus that the foot is 

 brought more or less directly forward in walking. As in the dino- 

 saurs there is a greater or less reduction of the postaxial fingers and 

 a strengthening of those on the other side of the feet. Only rarely, 

 in certain aquatic types, have the outer fingers of the hand more 

 than three phalanges, probably because of an incipient hyperpha- 

 langy. 



Regarding the general classification of the Chelonia there is still 

 dispute. According to Cope, Dollo, and Hay there are two chief 

 divisions or suborders, the Athecae and Thecophora, dependent upon 

 the character of the carapace, the former with but a single living 

 species, the latter with more than two hundred. The more generally 

 accepted classification recognizes four suborders, the Cryptodira (in- 



