564 



REPTILES. 



carapace, for this must tend to make respiration less active. 

 The lungs are divided into a number of compartments. 



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

 shells. 



Some Peculiarities in the Skeleton of Chelonia. 



The dorsal vertebras seem to be without transverse processes, and 

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

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



The greater part of the dorsal shield seems to be due to a coalescence 

 of rib-cartilages ; to an ossification of these 

 and of the surrounding intercostal tissue ; 

 and to a coalescence with superficial der- 

 mal bones. 



Similarly, the median pieces are the 

 result of fusion between median dermal 

 bones and the neural arches. The excep- 

 tional Athecce have been noted above. 

 The plastron pieces are comparable to 

 the "abdominal ribs" of the crocodile 

 or of the New Zealand lizard ; at the 

 same time, it is possible that the three 

 anterior pieces represent clavicles and 

 interclavicle. 



The cervical vertebras have at most 



little rudiments of ribs, are remarkably 



varied as regards their articular faces, 



and give the neck many possibilities of 



motion. There are no lumbar vertebras. 



The bones of the skull are immovably 



united ; 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 ; the premaxillas are veiy 



small ; there are no teeth ; there is a complete bony palate formed 



in great part from the junction of the pterygoids with the basisphenoid 



and with one another. 



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, pre- 

 coracoid. 



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. 



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. 242. — 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. 



