186 



KEPTILIA. 



are nearly hidden beneath the skin, and sometimes are wanting. The skin is 

 smooth, viscous, and furrowed by annular plaits or wrinkles ; it is apparently 

 naked, but on dissection we find in its thickness perfectly formed, though 

 delicate, scales, regularly arranged in several transverse rows between the folds 

 of the skin; a fact ascertained in the C. glutinosa ; the head of which is de- 

 pressed; the ribs much too short to surround the trunk; the articulation of 

 the bodies of their vertebrae is effected by hollow conical facets filled with a 

 gelatinous cartilage, as in fishes, and in some of the Batrachians with vegetable 

 matter ; earth and sand are also found in their intestines. 



ORDER IV. 



BATRACHIA *. 



THE Batrachians have a heart composed of but one auricle and one ventricle. 

 They all have two equal lungs, to which at first 

 are added branchia:, that have some affinity with 

 those of fishes, and which have cartilaginous 

 arches on each side of the neck attached to the 

 hyoid bone. Most of them lose these branchiae, 

 and the apparatus which supports them, when 

 they attain a state of maturity. Three genera 

 only, Siren, Proteus, and Menobranchus, retain 

 them for life. 



As long as these branchia? remain, the aorta is divided at its origin into as 

 many branches on each side as there are branchiae. The branchial blood is 

 brought back by veins which unite near the back in one arterial trunk, as in 

 fishes. It is from this trunk, or immediately from the veins which form it, 

 that arise most of the arteries which nourish the body, and even those which 

 conduct the blood to be oxygenated in the lungs. 



In those species, however, which lose their branchia?, the attendant arteries 

 are obliterated, with the exception of two, which unite in a dorsal artery, 

 giving, each, a small branch to the lungs. It is the circulation of a fish meta- 

 morphosed into that of a reptile. Batrachians have neither scales nor shell ; a 

 naked skin invests their body, and, one genus excepted, they have no nails. 



The envelope of the ova is membraneous. The eggs become greatly enlarged 

 in the water. The young not only differ from the adult in the presence of 

 the branchiae; but their feet are developed by degrees, and several species 

 have a beak and tail, which they subsequently lose, and intestines of a dif- 

 ferent form. 



Some species are viviparous. 



From jBarpaxoy (Prog), analogous to Frog*. 



