ORGANIZATIONOFREPTILES. 13 



The dermis, or true skin, varies a good deal. In the heads of the Chelonia it 

 is only seen as a thin fibrous lamina, closely applied to the bones over which it 

 passes. In the Frogs it is much more distinct, but is loosely connected vs^ith the 

 subjacent organs by means of vessels, nerves, «Sjc., the principal points of attach- 

 ment being at the extremity of the toes, and at the jaws and axiUa, the skin, as is 

 remarked by Dumeril,* forms a loose sac, in which the body of the animal is 

 placed. 



2. Digestive Organs. — Digestion is the most general, as well as the most 

 necessary function of living animals, both for their existence and the perfect per- 

 formance of their actions. A continual waste is experienced in the animal economy 

 which must be as constantly supplied. The aliment is the source from which this 

 supply is derived, food being necessary, as well for the restoration of organs as 

 for their developement. But the aliment, of whatever nature it may be, is not at 

 once admitted into the general mass of the circulating fluids; a series of chemical 

 changes are requisite for its perfect elaboration, and to produce these alterations. 

 Reptiles are provided with an alimentary canal. This, like the sac of the zoophyte, 

 is a prolongation or duplicature of the external covering of the body; simple in 

 some, more complicated in others; the kind of food nature has assigned the animal, 

 having an important influence on its internal organization. Almost all Reptiles 

 are carnivorous. Most of them feed on hving prey, seizing it when in motion, and 

 swallowing it without mastication. The Anolius, Frogs, Toads, and Hylse, feed 

 on insects — the Water-snakes, on Tadpoles, Frogs, or small Fish; other Serpents 

 hve on Squirrels, Rabbits, or even Birds, which they pursue with great activity 

 along the branches of trees. A few animals only of this class subsist entirely on 

 vegetable food, as the Green Turtle and Gopher. 



The alimentary canal begins at the mouth and terminates at the vent, and has 

 several important appendages. The mouth is generally large, the articulation of 

 the lower jaw being placed far back; and many have the power of increasing its 



* Hist. Nat. des Rept., torn. i. p. 6S. 



