40 ANATOMY AND PHYSIOLOGY 



mediately. On the other hand, if the gills are 

 forcibly kept open, so that no reaction can be ef- 

 fected upon the column of water on which the 

 mouth is exerting a pressure, death will also 

 ensue. 



Most of the lizards possess lungs, which are 

 long cylinders, extending through the whole ex- 

 tent of the body, but if their mouths be propped 

 open, they will assuredly die for want of air, 

 in a "little time, as they necessarily breathe 

 through their nostrils. The frog respires precise- 

 ly in the same way drawing the mouth full of 

 air, and when the pouch under the lower jaw is 

 thrust out with it, the reptile forces it into its 

 lungs, through a slit at the root of the tongue, 

 which is the glottis. Thus, the mouth of the 

 frog, toad, and all the lizards, is a bellows, to force 

 the air into the lungs. Breathing with them, is 

 an act of volition. This explanation will account 

 to the young reader, for the broad, flat heads of 

 this class of reptiles ; in this respect, there is a 

 curious analogy between them and the action of 

 the jaws of fishes. The one is a forcing pump, 

 as in the fish, for forcing the water suddenly 

 through the fringes of the gills, and the other, 

 a bellows for driving the atmospheric air into the 

 long slender lungs. The muscular force of the 

 sides and abdomen, soon presses it out again. 



