378 SNAKES. 



of the maxillary, the socket of the fang, and with it the 

 tooth itself, rotates in such a manner that the apex of 

 the tooth describes the arc of a circle, and finally points 

 downward instead of backward. This protrusion of the 

 fang is not an automatic motion, consequent upon the mere 

 opening of the mouth, as formerly supposed, but a volitional 

 act, as the reverse motion, viz. the folding back of the fang, 

 also is ; so that in simply feeding the fangs are not erected.' 

 (But I think I may affirm positively that sometimes the 

 vipers do use their fangs in feeding. When they open 

 their mouths— or rather the jaws alternately very wide — I have 

 seen first one and then the other fang occasionally engaged in 

 the food and again disengaged unsheathed. On other occasions 

 the fangs have been folded. In some large African vipers, 

 the ' River Jack' and others that were in the Society's Gardens 

 a few years ago, I was able to observe this easily.) 



The fang is folded back 'with an action comparable 

 to the shutting of the blade of a pocket-knife ; . . . one set 

 of muscles prepares the fangs for action, the other set stows 

 them away when not wanted. . . . The fangs are further 

 protected by a contrivance for sheathing them, like a sword 

 in its scabbard. A fold of mucous membrane envelops the 

 tooth like a hood. . . . The erection causes the sheath to 

 slip, like the finger of a glove, and gather in folds round 

 its base. ... It can be examined without dissection.' (And 

 with the naked eye in a large viper, even during life, you 

 may sometimes perceive this sheath or hood half off.) ' Each 

 developing fang is enclosed in a separate capsule,' says 

 Dr. Mitchel, which is just what I thought I saw in 'grovel- 

 Hng' up the poor Bushmaster's reserve fangs. There was 



