232 VEKTEBRATA: REPTILIA OR REPTILES. 



The tongue of serpents is long, slender, bifid, extensi- 

 ble, and retractile within a sheath ; the eyes are without 

 movable lids ; trachea very long ; lung single, and extend- 

 ing nearly the whole length of the body. 



Serpents cast their skins at least once a year. They 

 lay eggs with a flexible shell ; some of them, however, 

 are ovo-viviparous ; that is, the eggs are hatched while 

 still in the body of the parent. This is especially true of 

 venomous snakes. 



The Boa-Constrictor and Anaconda of South America, 

 the Pythons of Africa and the East Indies, constitute the 

 family of Boidse, huge serpents in some cases attaining 

 the length of thirty or forty feet, and capable of swallow- 

 ing dogs, sheep, and deer, after having crushed them in 

 their powerful folds. They have spur-like appendages as 

 rudiments of hind limbs. 



All of our most common species, as the Striped Snakes, 

 Water Snakes, Black Snakes, and a long list of allied 

 genera, belong to the family of Colubridse. They have 

 no rudiments of hind limbs. 



Rattlesnakes or Crotalidse and their allies are serpents 

 whose upper jaw contains but few teeth, but is armed 

 with sharp-pointed, movable poison-fangs. These fangs 



s 

 Head of a Rattlesnake. 



em, elevator muscles ; pg, poison gland ; n, nostril, beneath which Is a little 

 cavity or pit ; pf, poison tangs; s, salivary glands. 



