594 



REPT1LIA. 



The cloacal aperture is usually longitudinal, never trans- 

 verse ; the copulatory organ is unpaired. 



All are oviparous. The eggs have firm, usually calcareous, 

 shells. 



Some Peculiarities in the Skeleton of Chelonia. 



The (10) dorsal vertebrae are without transverse.or articular processes, 

 and along with the ribs are for the most part immovably fused in the 

 carapace. The tail and neck are the only flexible regions. There are 

 two sacral vertebrae. 



The greater part of the dorsal shield is due to a coalescence of eight 



ribs with eight costal plates derived from 

 the dermis. 



Similarly, the median pieces are the 

 result of fusion between median dermal 

 bones and the neural spines of the 

 vertebrae. The plastron usually consists 

 of nine dermal bones, and it is possible 

 that the three anterior pieces represent 

 clavicles and interclavicle. 



The eight cervical vertebrae have at 

 most little rudiments of ribs, are remark- 

 ably varied as regards their articular faces, 

 and give the neck many possibilities of 

 motion. There are no lumbar vertebrae. 

 The bones of the skull are immovably 

 united ; there is only a lower temporal 

 arcade, formed by jugal and quadrato- 

 jugal ; there are no ossified alisphenoids, 

 but downward prolongations of the large 

 parietals take their place ; neither pre- 

 sphenoid nor orbitosphenoids are ossified ; 

 there are no distinct nasal bones in modern 

 Chelonians, their place being taken by 

 the prefrontals ; the premaxillre are very 

 small ; there are no teeth. 



There is no sternum. The pectoral 



girdle on each side consists of a dorsal scapula attached to the carapace, 

 a ventral coracoid bearing terminally a small epicoracoid, and anterior 

 to the coracoid a precoracoid. The scapula and the precoracoid unite 

 to form one bone. 



The pelvic girdle consists of dorsal ilia attached to the carapace, 

 posterior ischia, and anterior pubes, with pre-pubic processes and an 

 epi- pubic cartilage. There is a pubic and an ischiac symphysis. 



The girdles originally lie in front of, or behind the ribs, but are over- 

 arched by the carapace in the course of its development. 



FIG. 289. Carapace of tor- 

 toise. From Edinburgh 

 Museum of Science and 

 Art. 



The dark contours are those of 

 the bony pieces ; the lighter 

 contours are those of the scales 

 which have been removed. 



