REPTILIA. 



form of a Fish respiring by branchisB^ to that of a Quadruped 

 breathing by lungs. Some of them, however, always retain 

 their branchiae, and a few have never more than two feet.(l) 



ORDER I. 

 CHELONIA. 



The Chelonia, better known by the name of Tortoises, have 

 a heart composed of two auricles, and of a ventricle divided in 

 two unequal cavities, which communicate with each other. 

 The blood from the body is poured into the right auricle, that 

 from the lungs into the left, but the two streams become more 

 or less mingled in passing through the ventricle. 



These animals are distinguished at the first glance by the 

 double shield in which the body is enveloped, and which al- 

 lows 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 denticu- 

 lated sutures, and with plates adhering to the annular portion 

 of the dorsal vertebra, so that all these parts are rendered 

 fixed and immovable. The inferior shell is formed of pieces, 

 usually nine in number, analogous to a sternum. (2) A frame 

 composed of bony pieces, which have been considered as pos- 

 sessing some analogy with the sternal or cartilaginous portion 



(1) The Sauria and Ophidia are differently arrang'ed by some others, Merrem, 

 for instance. They detach the Crocodiles, to form a separate order, and unite 

 the first family of the Ophidia or Angais to the remainder of the Sauria, a dis- 

 tribution which is founded on some peculiarities in the organization of Crocodiles, 

 and on a certain resemblance of Anguis to the Lizards. We merely indicate 

 these affinities, which are almost wholly internal, preferring a division more easily 

 applied. 



(2) See Geoff. An. du Mus. t. XIV, p. 5; and on the entire osteology of the 

 Tortoises, my IJech. sur les oss. foss. tom. V, 2e partie. [N.B. It is well to re- 

 mark, that I shall hereafter designate the upper shell by the single word shell 

 (testa) and the inferior by sternum. Jim. Ed.] 



