144 
GUIDE TO THE 
Echis carinata, and Daboia russellii; and the Pit Vipers 
or Crotalidce , to which sub-Family the Rattle-snake belongs 
and the Tree Vipers of which there are a considerable 
number of species in Eastern Asia. 
Such, then, is the variety of form and structure found in 
the Op hi dice which are an especially interesting group of 
animals owing to the deadly power possessed by many of 
them. Their habits of life also are quite as varied as their 
forms, and it has been shown that some live in water as well 
as on land. The fresh-water snakes are all harmless, while 
the sea snakes are all poisonous and deadly as a rule. The 
mouth of serpents generally is provided with a long 
forked black tongue which is being constantly exerted and 
retracted while the animal is on the alert, and it is a per¬ 
fectly harmless organ. The poisonous snakes are furnish¬ 
ed with fangs by means of which the poison is intro¬ 
duced into the system of the animal bitten. The poison 
is the product of a gland lying below and behind the eye, 
and the poisonous saliva secreted by this structure is 
conveyed to the fang by means of a duct or tube that leads 
either to a groove in the front of the tooth, or to a canal in 
the tooth itself formed by the inward folding of its margins, 
and, as the snake bites, the poison is introduced into the 
wound made by the two teeth of the upper jaw which 
are so modified, and its introduction is facilitated by the 
contraction of the duct and by the pressure of the muscles 
of the jaw on the gland as the mouth is opened and shut. 
The snakes which have the groove in front of the fang 
belong to the Colubrine division of the Poisonous snakes, 
and in general appearance do not differ much from the 
Harmless snakes, whereas the Hollow-toothed poisonous 
snakes constitute the Viperine section already indicated, 
