38S CLASS REPTILTA. 



THE FOURTH ORDER OF REPTILES. 



The Batrachia, 



Have but a single auricle and a single ventricle to 

 the heart. They all have two equal lungs, to which 

 are united in their early age, gills which have some 

 relation with those of fishes, and which have, on 

 the two sides of the neck, cartilaginous arches, 

 which are attached to the hyoid bone. The majo- 

 rity of them lose these gills, and the apparatus 

 which supports them, when they arrive at the 

 perfect state. Three genera only, the siren, the 

 proteus, and menobranchus, preserve them all their 

 lives. 



As long as the gills subsist, the aorta proceeding 

 from the heart is divided into as many branches on 

 each side as there are gills. The blood of the gills 

 returns by the veins, which unite towards the back 

 in a single external trunk, as in the fish. It is from 



