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 FlG - 254 - 

 union of the ribs and dorsal 

 vertebrae, and is known as 

 the carapace. It is joined 

 to the lower shield, called i;|p 



plastron, by bands of bony TORTOISE. Its body is enveloped in 



' / a solid box, called a shell, 



pieces. The 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- 



