CHELONIANS. 457 



nine bony portions, of which eight are in pairs ; the ninth is 

 single, and occupies the front part of the plastron. 



(2) The Chelonians are also distinguished from other Reptiles 

 by the entire absence of teeth. As a compensation for this, 

 however, the jaws are cased in horny coverings with cutting 

 edges, resembling the hooked beak of a Parrot, and with which 

 they crop and mince the vegetable substances on which many 

 of them feed. The armor in which the animals are encased, 

 seems to be their most effectual defence. In the Land Tortoises 

 the carapace is usually much arched and firmly united, so that, 

 without injury, it can sustain a very great weight; the plastron 

 in these also exhibits the highest degree of solidity, and is united 

 to the carapace by an extended lateral surface. At the line of 

 its union, it is sometimes slightly movable, but in most, it is 

 fixed by an unyielding suture. Its front and hind margins are 

 generally indented or notched, for the more easy egress of the 

 neck and tail ; but sometimes they simply end in a cross line ; 

 or, on the contrary, are prolonged into a point. In the Land 

 Tortoises of the genus Pyxis, (Gr. puxis, a box,) species Arach- 

 noides, (Gr. spider-like,) the Arachnoid Tortoises of India, the 

 plastron is furnished with a transverse hinge, giving a power 

 of motion to the front part, so that the animals can redraw their 

 head and fore-limbs within the carapace, and close the plastron 

 upon it. In another genus of the same group, Cynixis, of Guiana, 

 the carapace, instead of being one solid whole, has the posterior 

 portion distinct from the front portion, and movable, so as to close 

 upon the hinder margin of the plastron, and shut in the hinder 

 limbs and tail. In the aquatic species, the shell is generally 

 more flattened, so as to present less resistance to the water. 

 Some of them swim with considerable rapidity, and are much 

 more active in their habits than others of the order. The shell 

 of such has its parts less firmly united, and is, in some degree, 

 flexible ; it also affords much less complete protection to the 

 body. 



Notwithstanding the horny beak with which the jaws of Tor- 

 toises are in general furnished, the sense of taste is decidedly 

 higher in these than in other Reptiles. The broad, thick, fleshy, 

 and movable tongue, is provided with salivary glands, and nerves 

 of taste, but is not capable of being protruded from the mouth. 

 It is not an organ of taste merely, but filling out the entire cavity 

 of the mouth, assists in the process of respiration ; for " Turtles 

 swallow the air they breathe." 



The eyes are larger in proportion, and more movable in 

 Tortoises than in other Reptiles. They have three eye-lids ; two 



