THE REPTILES 275 



sharp, incurved teeth on three sets of jawbones, any of which 

 will grow again to replace those that may be broken or torn out. 

 The lower jaw is not fixed directly to the skull, but is attached 

 to a separate bone, the quadrate, which in turn is attached to the 

 skull, thus permitting the jaw to move forward and backward, as 

 well as up and down. This enables the snake to literally crawl 

 outside of its victim, the upper teeth holding firmly while the 

 lower jaw is advanced; then the upper jaw takes a new hold, and 

 so on. The process is slow, often occupying hours, but there is 

 no chance for escape of the prey. The snake's teeth cannot bite 

 the food in pieces, so all its victims must be swallowed whole. 

 To permit this, the various bones of the skull, so solid in other 

 animals, are loosely attached in the snake, allowing the head to 

 expand when swallowing is taking place. The two halves of the 

 lower jaw are attached together by an elastic ligament which 

 allows them to open sidewise, so that the lower jaw is capable of 

 three motions, up and down, back and forward, and (each half) 

 sidewise. 



The process of swallowing is so long that special adaptations 

 are provided to permit breathing to go on. The trachea may be 

 extended along the floor of the mouth, almost to the teeth, so that 

 air may reach the lungs, and moreover there is a large air chamber 

 behind the lung to store air for this purpose. 



The gullet and stomach are highly elastic and the digestive 

 fluids very active, to accommodate food in such large doses. The 

 flexible ribs and lack of breast bone or limb girdles allow for the 

 passage of these enormous mouthfuls. 



The delicate and slender forked tongue is protected during 

 swallowing by being retracted into a sheath. Its function is for 

 touch, rather than taste, which sense would be of very little use 

 to an animal which eats its food whole and sometimes alive. 



Snakes obtain their food in three general ways: they may catch 

 it with the teeth and swallow it at once as does the common garter 

 snake; they may crush the prey in their coils, before swallowing, 

 as do all constrictors ; or they may have poison apparatus developed, 

 which stupifies or kills their victim immediately. 



