150 VITAL FUNCTIONS. 



part, that the air is swallowed, and forced down the 

 trachea into the lungs. 



The aperture leading from the mouth to the lungs, is 

 through the middle of the back part of the tongue. Fig. 



Fig. 93. 



93 represents this odd apparatus ; a the tongue, d the 

 orifice to the trachea, c the throat, and b the nostrils. 

 The tongue is not attached far back in the throat, like 

 that of other animals, but lies fixed to the lower jaw, or 

 chin, so as to increase its length out of the mouth. If 

 the mouth of a Frog be forcibly kept open, the creature 

 is soon strangled, because the aperture through the 

 tongue is not only thus closed, but were it open, there 

 would be no respiration without the action of the bel- 

 lows, which by opening the mouth is destroyed. 



This is the mode in which most of the reptiles perform 

 their respiration, the process being that of swallowing 

 the air, rather than breathing it, as other animals do. 



RESPIRATION IN BIRDS. 



In Birds the respiratory apparatus is quite different 

 in most respects, from that of reptiles. There is also a 

 remarkable difference in the mode in which the process 

 is performed. 



In these races, the air does not merely pass into the 

 lungs, but is drawn through them, into the large air cells 

 which are contiguous. This is done by elevating the 



How does the respiration of the frog differ from that of other animals 1 



