320 THE VITAL FUNCTIONS. 



whole length of the body. The lung on the left 

 side is in general scarcely discernible, being- 

 very imperfectly developed. In the Chamelion 

 the lungs have numerous processes which pro- 

 ject from them like caeca. In the Sauria, the 

 lungs are more confined to the thoracic region, 

 and are more completely cellular. 



The mechanism, by which, in these animals, 

 the air is forced into the lungs, is exceedingly 

 peculiar, and was for a long time a subject of 

 controversy. If we take a frog as an example, 

 and watch its respiration, we cannot readily dis- 

 cover that it breathes at all, for it never opens 

 its mouth to receive air, and there is no motion 

 of the sides to indicate that it respires; and 

 yet, on any sudden alarm, we see the animal 

 blowing itself up, as if by some internal power, 

 though its mouth all the while continues to be 

 closed. We may perceive, however, that its- 

 throat is in frequent motion, as if the frog were 

 economising its mouthful of air, and transferring 

 it backwards and forwards between its mouth 

 and lungs ; but if we direct our attention to the 

 nostrils, we may observe in them a twirling 

 motion, at each movement of the jaws ; for it is, 

 in fact, through the nostrils that the frog receives 

 all the air which it breathes. The jaws are 

 never opened but for eating ; and the sides of 

 the mouth form a sort of bellows, of which the 

 nostrils are the inlets ; and by their alternate 



