BACKBONED ANIMALS WHICH BREATHE IN AIR 



425 



and which is separated by a fold from the mouth-cavity. The 

 mouth can therefore be kept open under water without fear of 



Fig. 549, — Head of Crocodile to show Breathing Arrangements, hinder part in section 



BR., Brain: LA., larynx; L.J., lower jaw; n,, external nostril; n'., internal nostril; SK., skull. Course of 

 air entering lungs shown by arrows. 



of water into the lungs. The external 

 and close when their owner sinks below 



suffocation by entry 

 nostrils are valvular, 

 the surface. 



Curious modifications of the breathing-organs 

 are found in Snakes. As in the snake-like Amphi- 

 bians (Caecilians), the left lung is reduced to a 

 mere vestige, the right lung being correspondingly 

 enlarged. The reason for this arrangement would 

 appear to be the same in both cases, i.e. adapta- 

 tion to the shape of the long narrow body. An 

 ordinary Snake feeds on living animals of rela- 

 tively large size, and, to prevent choking while 

 the tedious process of swallowing is going on, the 

 end of the windpipe is drawn out into a project- 

 ing tube which protrudes from one side of the 

 mouth. 



Snake-like Lizards {AmphisbcEiia), like true 

 Snakes, possess but one fully-developed lung, that 

 of the right side. 



The lungs of Chameleons (fig. 550) suggest 

 the arrangements that Birds possess in a much 

 more elaborate condition, for the hinder portions of them grow 



Fig, 550.— Lungs of 

 a Chameleon, showing 

 outgrowths. TR. .Wind- 

 pipe (trachea). 



