VIPERINE FANGS. 375 



of experiments with the venom and the treatments adopted. 

 But of especial interest here are his observations on the fangs 

 and their voHtional action, it having previously been supposed 

 that the mere opening of the mouth brought the fangs into 

 position, which is not the case. As the Crotahis can move 

 each side of its mouth independently, so it can use one or 

 both fangs. ' When the mouth is opened widely, it still has 

 perfect control over the fang, raising or depressing it at will.' 

 Dr. Mitchel saw that though both fangs were present, both 

 were not always used. When a viperine snake yawns ex- 

 tensively, as it so often does, you may sometimes perceive 

 the fangs partially erected or entirely so, or the ' vibratile 

 motion ' in them observed by Fayrer. When the snake is 

 angry, this vibratile action is much like that of a cat gnashing 

 the teeth ; but when only in a yawn, the partial and unequal 

 erection of one or both fangs has the appearance of being 

 involuntary. In this I speak from observation. The effect 

 is similar to that seen about a person's mouth in trying to 

 suppress a yawn — a sort of convulsive, nervous twitching. 

 Whatever the cause, you perceive the fangs moving, but 7iot 

 moving always in accord. 



The shedding or replacement of the fangs is. Dr. Mitchel 

 thinks, a regular process, as in the teeth of some fishes, 

 though not regular as to time. Sometimes, but not always, 

 they are shed with the casting of the cuticle. He 'cannot 

 suppose that the almost mature secondaries are awaiting 

 an accident ; ' which agrees precisely with the opinions of 

 Dr. Edward Nicholson and other physiologists quoted in 

 the last chapter : ' A crop of young teeth ' (or of fangs) 

 'work their way into the intervals of the old teeth, and 



