146 VITAL FUNCTIONS. 



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

 into the lungs. 



440. The aperture leading from the mouth to the 

 lungs, is through the middle of the back part of the tongue. 

 Fig. 93 represents this odd aparatus ; a the tongue, d the 



Fig. 93. 



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 bellows, which by 

 opening the mouth is destroyed. 



441. This is the mode in which most of the reptiles per- 

 form their respiration, the process being that of swallowing 

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



RESPIRATION IN BIRDS. 



442. 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. 



443. In these races, the air does 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? 



