THE POISON FANGS. 25 



motionless upon water, apparently lying on it as lightly as a cork, 

 sunning themselves in the hot rays of the midday sun. On being 

 alarmed, they instantly sank out of sight without any apparent 

 muscular effort. This is partly accomplished by expelling the air 

 from the long, tube-like lung, whereupon the body sinks, being 

 then denser than the water. 



The Poison Fangs. 



In the typical venomous snakes, the outer row of upper teeth 

 has vanished, with the exception of fangs, more or less large, 

 and set in the front part of the upper jaw. These fangs are 



.D 



r 



ANATOMY OF THE HEAD OF A VENOMOUS SNAKE. 

 Fig. 15. — A. Duct from the poison gland, the end of which is bent upon itself and 

 resting in the hole at the base of the fang' into which the venom is squirted. 



B. Digastric muscle which opens the jaw. 



C. Poison gland. 



D. Point of junction of the squamosal and quadrate. 



E. Anterior temporal muscle. 



F. Posterior temporal muscle. 

 H. The bifid tongue. 



I. Lower jaw in which some solid recurved teeth are set. 

 d. Trachea or windpipe. 



either deeply grooved or hollow, and are connected by a channel 

 or duct with the poison glands, which secrete the venom. The 

 poison glands, with but one or two exceptions, lie one on each side 

 of the head, just below and back of the eyes. These glands are 

 almond-shaped, and vary in size according to the species of snake. 

 In the Puff Adder they are about the size of a small almond. 

 The venom is secreted by the cells composing the gland, and is 

 expelled through the duct, down the grooved or hollow fangs 

 into the punctures when the snake bites. The venom is driven 

 out of the glands by the constriction of certain muscle fibres 

 which compress the glands violently. 



