240 BRANCH CHORDATA 



or subterranean, while still others are arboreal in their habits and 

 habitat. 



The color of snakes is usually brownish or green, which affords 

 a good protective resemblance to the ground or grass upon which 

 they creep. 



The skin is scaly. The horny epidermis is shed from one to 

 several times yearly, the whole outer skin, from lips to tail, being 

 turned wrong-side out, even to the transparent covering of the 

 eyes. The first molting takes place "within forty-eight hours 

 after birth" before the young snake begins to feed. In the 

 rattlesnake, at each time the skin is shed, "there is left a ridge 

 or rim of it at the tail, which forms the rattle." 



Food. — Since there are no limits for prehension, snakes must 

 depend upon the mouth to secure the prey, which is swallowed 

 whole. The constrictors, like our common blue racer and the 

 boa constrictor, wind their bodies about their victims and 

 literally squeeze them to death. The teeth point toward the 

 throat, thus preventing the escape of the prey from the mouth. 

 The snake has also a distensible lower jaw, enabling it to swal- 

 low an animal as large or larger than the diameter of the snake's 

 own body. The bones and palatal apparatus are united by 

 ligaments only, thus allowing them to spread apart in the 

 process of swallowing. An abundant supply of saliva (which 

 appears first in reptiles) renders swallowing the more easy. 



Snakes are carnivorous, feeding upon mice, birds, frogs, and 

 insects. Poisonous snakes should l)e killed, of course, but the 

 non-poisonous ones are quite useful in the fields in destroying 

 vegetable-feeding animals, especially rodents and insects. 



Respiration is mainly by one lung, the other one being 

 rudimentary. The trachea may be slightly protruded between 

 the halves of the lower jaw during the process of swallowing, to 

 prevent suffocation. 



Senses and Intelligence. — The eyes are not movable nor have 

 they a movable eyelid, hence their glassy stare. The lacrimal 

 fluid passes internally into the nasal cavities. No external ear 

 is visible, though the hearing is good. The sense of smell is 

 well developed, some snakes being greatly aided by it in their 

 search for prey. The tongue, which is slender, forked, and 

 sheathed, is protractile, moist, and very sensitive to touch. 



