CHELONIA. 169 



The Sauria, or Lizards, whose heart has two auricles, and whose 

 body, supported by four or two feet, is covered with scales. 



The Ophidia, or Serpents, whose heart has two auricles, and whose 

 body always remains deprived of feet. 



The Batrachia, whose heart has but one auricle, and whose body is 

 naked, most of which pass, with age, from the form of a Fish respiring 

 by bronchiae, to that of^ a Quadruped breathing by lungs. Some of 

 them, however, always retain their bronchiae, and a few have never 

 more than two feet. 



ORDER I. 



CHELONIA. 



THE Chelonia, better known by the name of Tortoises, have a heart com- 

 posed of two auricles, and of a ventricle divided 

 in two unequal cavities, which communicate 

 with each other. 



These animals are distinguished at the first 

 glance by the double shield in which the body 

 is enveloped, and which allows no part to project 

 except their head, neck, tail, and four feet. 

 The shell (or upper shield) is formed by the ribs, 

 of which there are eight pair, widened and 

 reunited by denticulated sutures, and with plates adhering to the annular 

 portion of the dorsal vertebrae, so that aU these parts are rendered fixed 

 and immoveable. The inferior shell is formed of pieces, usually nine in 

 number, analogous to a sternum. A frame composed of bony pieces, which 

 has been considered as possessing some analogy with the sternal or cartilagi- 

 nous portion of the ribs, and which in one subgenus always remains in a car- 

 tilaginous state, surrounds the shell, uniting and binding together all the ribs 

 which compose it. The vertebra of the neck and tail are consequently the 

 only ones which are moveable. 



The lungs have considerable extent, and are situated in the same cavity 

 with the other viscera. The thorax in most of them being immoveable, it is 

 by the play of its mouth that the tortoise respires, which it effects by keeping 

 the jaws closed, and alternately raising and depressing the os hyoides. The 

 former of these motions permits air to enter through the nostrils, the tongue 

 then closes the internal orifice of those apertures, when the latter forces the air 

 into the lungs. 



Tortoises have no teeth ; their jaws are invested with horn like those of 

 birds ; the Chelydes excepted, where they are covered with skin only. 



They possess great tenacity of life, and instances are on record in which they 

 have been seen to move for several weeks after losing their head. They require 



