536 TORTOISES. 



TORTOISES. 



Tortoises (Testudinata, or Chelonians) belong to a very 

 numerous order of reptiles, the usual form of which is too 

 well known to require description. They are shut up, as it 

 were, in a box and breast-plate : the carapace and plastron, 

 in reality, are external developments of certain parts of the 

 skeleton. 



The land tortoises have the strongest plastrons. In some 

 species it is slightly movable, but generally fixed by a uniting 

 suture. In one the pyxis the plastron is furnished with a 

 transverse hinge, so that the animal can retract its head and 

 fore-limbs within the carapace, and close the plastron upon it, 

 first shutting them in. In another the kinixis the carapace 

 has the posterior portion distinct from the anterior, and mov- 

 able, so as to shield the hind-limbs and tail. 



In water tortoises, or turtles, as they are generally called, 

 the plastron is united to the edges of the carapace by inter- 

 vening cartilage, and not by suture. The jaws of tortoises 

 are not furnished with teeth, but are cased in horny coverings, 

 resembling somewhat the sharp hooked beak of a parrot ; which 

 enable them either to crop and mince the vegetable aliment 

 on which most of them live, or to masticate the small, living 

 animals, such as birds and reptiles, of which the food of others 

 consists. Round the outside of this beak are thick fleshy lips. 



In the curious matamata, the jaws of which open very 

 wide, these parts, instead of being armed by a strong beak, 

 are protected by a sheath of horn. 



In the land tortoises, the feet are stump-like, the toes being 

 enveloped in the skin, so that they can move but slowly. 

 The marsh and lake tortoises have their feet palmated, to en- 



