54 NATURALIST'S CABINET. 



Curious mode of respiration. 



the jaws during this action are kept closely lock- 

 ed into each other by grooves; for if the mouth 

 be kept open it cannot respire at all, and the 

 animal will presently be seen struggling for 

 breath. When observed carefully, a frequent 

 dilatation and contraction may be seen in the 

 skinny bag-like part of the mouth which covers 

 the under jaw. From this it would appear, at 

 first sight, as if the creature lived all the while 

 on one mouthful of air, which it seems to be 

 playing backwards and forwards betwixt its 

 mouth and lungs ; but for each movement in the 

 jaw a corresponding twirling movement may be 

 observed in the nostrils. The mouth seems 

 therefore to form a sort of bellows, of which the 

 nostrils are the air-holes, and the muscles of the 

 jaws by their contraction and dilatation make 

 the draught. The nostrils are so situated that 

 the least motion on them enables them to per- 

 form the office of a valve. By the twirl of the 

 nostril the air is let into t*he mouth, when a dila- 

 tation of the bag takes place; it is then emptied 

 from the mouth, through the slit behind the 

 tongue, into the lungs, where there is a slight 

 motion in the sides of the animal, and the mus- 

 cles of the abdomen again expel it; and soon 

 afterwards a second twirl in the nostrils takes 

 place, and the like motions follow. Thus it ap- 

 pears that the lungs are filled by the working of 

 the jaws, or, in other words, that frogs swallow air 

 much in the same manner that we swallow food. 



