390 CLASS REPTILIA. 



The Frogs, Rana, Lin., 



Have four legs and no tail in their perfect state. 

 Their head is flat, their muzzle rounded, their 

 mouth greatly cleft. In the majority the soft tongue 

 is not attached to the bottom of the mouth, but to 

 the edge of the jaw and folds back within. The 

 front feet have but four toes, the hinder sometimes 

 exhibit the rudiments of a sixth. 



Their skeleton is entirely destitute of ribs. A 

 cartilaginous plate on a level with the head, is in 

 lieu of a tympanum, and enables us to recognize the 

 ear without. The eye has two fleshy lids and a 

 third concealed under the lower one, transparent 

 and horizontal. 



The inspiration of air is performed only by the 

 movements of the muscles of the throat, which, 

 dilating, receives the air through the nostrils, and 

 contracting while the nostrils are cleared by means 

 of the tongue, obliges this air to penetrate into the 

 lungs. Expiration on the contrary is performed by 

 the muscles of the abdomen ; thus when the belly 

 of one of these animals alive is opened, the lungs 

 dilate without being able to sink down, and if one 

 of them be forced to keep its mouth open, asphyxy 

 takes place, because the air of the lungs cannot be 

 renewed. 



The act of coition continues for a long time ; 

 there is a spungy sort of swelling on the thumbs of 

 the male, which increases during the spawning time. 



