CARNIVOROUS AND INSECTIVOROUS REPTILES 81 



When the mouth of a viper is closed the poison-fangs are 

 backwardly-directed and pressed closely against the palate, but 

 when the mouth is opened a series of slender bones running 

 forwards from the joint of the jaw pushes the movable upper- 

 jaw-bone forwards, causing the fangs to be " erected", i.e. rotated 

 downwards and forwards, so that they are ready for use. Closure 

 of the mouth reverses the action, enabling the snake to " strike " 

 or bite its prey. As, too, the fangs are very brittle, and therefore 

 liable to be broken off, a number of small " reserve fangs " are 

 imbedded in the jaw at the base of the one actually in use, and 

 these grow up one after another as required. 



Poisonous snakes even more than some of the harmless kinds 

 are accredited with powers of ' ' fascination "; in other words, 

 they appear to be able to hypnotize their prey. It has been 

 suggested that the rapid movement of the tongue may play an 

 important part in this process, just as in the human subject a 

 state of trance can often be brought about by gazing at a rapidly- 

 revolving mirror or " lark-mill". 



Some of the venomous serpents are so coloured and marked 

 that they harmonize with their surroundings; a case of " aggressive 

 general resemblance ", so called because it aids them in their 

 pursuit of prey, which are thus apt to be caught unawares. 



VOL. II. 38 



