300 THE WORLD OF ANIMAL LIFE 



VIPERS (Family ViPERlD^) 



The Adder, which is the third British snake, is a good type of 

 the Viper family. It may easily be distinguished from the two 

 already mentioned by the zigzag chain of lozenge-shaped black 

 markings which runs along the spine. 



This snake lives chiefly upon heaths and sandy commons, and 

 is fond of lying coiled up in the sun, in which position it bears so 

 strong a resemblance to a piece of twisted stick, that a passer-by 

 might easily tread upon it before discover- 

 ing its real nature. It is a venomous snake, 

 and a wound from its poison-charged fangs 

 is sufficient to cause serious illness, and 

 has occasionally been known to result even 

 in death. 

 Head and Tail of Common ^he fangs of a viper are very curiously 



Viper formed. They are situated in the upper jaw, 



one upon either side, and lie back upon 

 the roof of the mouth when they are not required for use. Were 

 it not for this provision, the snake would experience great difficulty 

 in swallowing its food. Each fang, however, is surrounded by 

 strong muscles, which throw it forward when the head is raised to 

 strike, and hold it firmly in position until after the blow has been 

 delivered. 



Just behind the sharp point of each fang is a tiny hole, shaped 

 somewhat like the eye of a needle. This hole opens into a channel 

 which runs through the tooth, and communicates at its base with 

 a small sac, or vessel, in which the poison is contained. It will 

 thus be seen that, when the stroke is delivered, the pressure upon 

 the tooth forces a small drop of poison out of the sac and through 

 the channel, and so into the flesh of the victim. 



The poison fangs of a viper are nearly transparent, and are 

 almost as brittle as glass. If one of them should be broken, 

 however, there is always a new one lying beneath it in readiness 

 to take its place. If the head of a viper be carefully dissected, 



