TORTOISES. 299 



CHAPTER XXXI. 

 Reptiles and Batrachians. 



THE reptiles are classified in five orders, as follows : 



1. Chelonia : having limbs and bodies usually covered 

 with horny scales ; the jaws terminate in a horny beak : 

 tortoises and turtles. 



2. Rhyncocephalia : only one representative, New 

 Zealand sphenodon. 



3. Lacertilia : bodies having limbs and covered with 

 scales ; teeth : lizards, chameleons, etc. 



4. Ophidia : no limbs, scales, teeth : snakes. 



5. Crocodilia : much like the lacertilia, but the heart 

 has four cavities as in the birds : crocodiles and alli- 

 gators. 



CHELONIA. 



Tortoises have a horny beak, analogous to that of 

 birds. The body is covered by a carapace, which forms 

 a sort of double shield protecting the entire trunk, and 

 within which the head, tail, and limbs can be drawn 

 when necessary. The up- 

 per shield is formed by the 

 union of the ribs and dorsal 

 vertebrae, and is known as 

 the carapace. It is joined 

 to the lower shield, called 



plastron, by bands Of bony ToRTOisE.-Its body is enveloped in 

 rp/ a solid box, called a shell. 



pieces. Ine motor muscles 



of the limbs and shoulder and the pelvis are enclosed 



in the carapace. 



The union of the ribs renders the mechanism of res- 



