48 Vertebrata. 



closed position of the mouth,while in the gaping state 

 they project, being arched downwards, ready to be 

 inserted into the victim about to be struck. The 

 groove in the tooth leads into a canal which traverses 

 the base of the poison fang, and is continued by a 

 duct into a cavity or sac, which receives the tubular 

 ducts of the poison gland (fig. 20). In the act of 

 striking, the muscles which close the jaws squeeze the 

 poison sac and drive the poison through the duct into 

 the tooth, and thence into the wound. 



The poison apparatus is constructed on the same 

 plan in the common viper (Pelias berus), not uncom- 

 mon in Central and Southern Europe, and easily re- 

 cognised by its dark green colour, and by the zigzag 

 black line in the middle of the back. Other poisonous 

 snakes like the asp, the cobra di capello, and the coral 

 snake, have other solid teeth coexisting with the poi- 

 son fangs, and some, like the dipsads, tree snakes, and 

 sand snakes, have some of the hinder teeth grooved. 

 The poison of snake-bites is rapidly fatal, death 

 taking place within an hour in general, and it is com- 

 puted that over 10,000 deaths take place annually 

 from this cause among human beings. 



The water snakes inhabit the Pacific and Indian 

 Ocean, and have flat tails. They possess strong un- 

 grooved teeth behind the true poison fangs. In one 

 species, allied to the coral snake ( Callophis inttstinalis), 

 the poison gland extends into the abdomen. 



One curious group of non-poisonous snakes pos- 

 sess teeth on the anterior surface of the neck vertebrae 

 in addition to feeble jaw teeth. These animals feed 

 on eggs, and use these teeth for breaking them while 



