24 



REPTILES AND BATRACHIANS. 



and in a sheath. The aperture is then exactly opposite, and 

 close to, the nostrils, through which only a snake breathes. 

 Should you happen to see one yawning, which it not unfrequently 

 does, you will be able to observe the two apertures, and probably 

 both in action ; that for the egress of the tongue, close to the 

 chink in the lip for its exsertion, and that of the windpipe just 

 behind and upon the tongue sheath. 



The elongated form of snakes causes corresponding variations 

 in their principal organs. One lung (the other is only rudiment- 

 ary) occupies nearly two-thirds of the body ; the trachea convey- 

 ing air into this is also much lengthened. So are the liver, the 

 oesophagus, and the stomach, etc. There are yet other remark- 

 able modifications in a snake's anatomy, adapting its structure to 

 its habits and requirements. The bones of the head, and 

 particularly those of the lower jaw, are "loose," i.e., united only 

 by elastic ligaments instead of being consolidated as in mammals ; 

 and are thus easily separable, stretching apart, enabling the 

 reptile to swallow food of much greater bulk than itself. Snakes 

 feed seldom, and no wonder, for the process cannot be agreeable. 

 Fortunately for them their sense of taste is dull, as they have no 

 means of freeing their prey from its fur or feathers. Luckily, too, 

 their digestion is powerful, as the prey must be swallowed as it is, 

 bones and all. The constricting snakes can retain an animal in 

 their coils till they are ready to swallow it ; the venomous snakes 

 can kill with the poison fang and wait their time ; but many 

 others, like our two little English snakes, can neither constrict nor 

 poison, but must hold their prey in their mouth when caught and 



a 



c 



Fig. 7. — Interior of the roof of the mouth, the upper jaws. Do 



s represent the teeth. 



not let go for a single instant, or it would escape. The teeth 

 are great assistants, being numerous, very long and fine, and all 



