DIVISIONS OF REPTILIA. 267 
fang, and is connected with the duct of the “ poison-gland.” 
This is a gland, situated under and behind the eye, secreting 
the poisonous fluid which renders the bites of these snakes dan- 
gerous or fatal. When the serpent strikes at any animal, the 
poison is forced through the poison-fang into the wound, partly 
by the contractions of the muscular walls of the gland, and partly 
by the compressive action of the muscles of the jaws. In some 
other snakes, several of which are not certainly known to be 
venomous, there are large grooved fangs placed far back in the 
mouth upon the upper jaw. 
Of the non-venomous harmless snakes, we have an excellent 
instance in our common Ringed Snake (Coluber natrix), which 
is of frequent occurrence in most parts of this country. Like all 
the snakes, it is strictly carnivorous, having a special liking for 
frogs, which it swallows whole. It oftentakes to the water, and 
can swim rapidly and gracefully, though in this respect it is ex- 
celled by the true venomous water-snakes (Wydrophide), which 
are adapted to an aquatic life by having a compressed swim- 
ming-tail, Other non-venomous snakes, such as the Boas and 
Pythons, though destitute of poison-fangs, are nevertheless 
highly dangerous and destructive animals. Their bite is harm- 
less, and they seize their prey by coiling themselves round it in 
numerous folds. By gradually tightening .these folds, they 
reduce their victim .to the condition of a shapeless bolus, which 
they finally proceed to swallow whole. In this way, a large 
Python or Boa will certainly succeed in disposing of an animal 
as large as a sheep or calf; and it has been asserted that human 
beings, and even oxen, can also be swallowed by unusually large 
specimens of this family. 
The Boas and Pythons have a horny spur on each side of the 
vent, and the tail is prehensile. Their dental apparatus is 
extremely powerful, giving them a firm hold for the constriction 
of their prey. They are the largest of all. the serpents, attaining 
a length of thirty to forty feet. The true Boas and Anacondas 
belong to the New World, but the Pythons are confined to 
India, Africa, and the Indian Archipelago. 
The poisonous snakes are represented by the Cvofalide of 
the New World and the Vzferide of the Old World. The 
common Rattlesnake (Crotalus horridus) of the United States 
has the extremity of the tail furnished with a “rattle” or horny 
appendage composed of several membranous cells of a pyramidal 
