98 BRITISH SERPENTS. 



bone, has the fang alone upon it. The adder-fang 

 is about one-third of an inch in length, curved back- 

 wards, the extremely fine point directed to the throat. 

 The fangs lie horizontally in a groove when at rest, 

 and only assume the vertical attitude when the adder 

 is about to strike. They can be moved independently 

 of each other, one or both being brought into play as 

 the adder wishes. When the adder is about to strike 

 the lower jaw is opened, the pterygoid goes forwards, 

 the os transversum rotates the maxilla (or upper jaw), 

 and the fang is brought into the striking position. 



The gland which secretes the venom is situated 

 at the base of each fang, and has a duct leading from 

 it to the narrow canal through the fang, which has 

 its point of exit just above the sharp point of the fang. 

 In the adder this canal is a closed one, while in some 

 other poisonous species it is merely a groove on the 

 surface of the fang. The poison, which is a chemical 

 one, is driven through the duct and down the canal by 

 the action of the muscles of the lower jaw, the whole 

 process being the work of a moment. 



When broken off or worn out, the fangs are quickly 

 replaced by others, the new ones being already de- 

 veloped and lying in the fang-sheath until required. 

 If the adder's jaw be opened widely (after death) and 

 the fangs carefully moved into the striking attitude, 

 the reserve supply of new fangs can be readily seen 

 with the naked eye. (For the effect of the bite see 

 later.) 



