POISON APPARATUS OF VENOMOUS SNAKES 69 



The whole process deepening the wound, fixing the prey, and injecting 

 the venom is the work of an instant, and the next effort of the snake is to 

 disentangle itself from the victim. This step is effected by relaxing the 

 muscles of the neck, so as to leave the head passive, while the continued trac- 

 tion of the muscles of the body pulls upon it and withdraws the fang. The 

 elastic mucus sheath glides over the fang, and the pterygoid externus, again 

 acting, depresses the latter, the snake resuming its posture of defense. 



It is not uncommon that in a bite but one fang takes effect. Again, it has 

 often been observed that when the snake in captivity is allowed to bite upon 

 the inner edge of a cup it often uses only one fang. Or, the fangs are used 

 alternately with intervals. It may happen that when the object stands too 

 near the snake the latter miscalculates the distance and the fangs are not in 

 the erect position, hence no penetration. In a contrary instance, the object 

 may be beyond reach of the snake and the biting movements may be per- 

 formed before the object is struck. In this case the venom is sometimes pro- 

 jected several feet. 



The traction of the anterior temporal muscle is associated with the com- 

 pression of the poison gland, and it becomes rather questionable how in a 

 pacific mood the snake prevents the flow of the venom when it uses this 

 muscle for other than the biting purpose. According to Weir Mitchell this 

 is prevented by two means: the most effectual is the sphincter around the 

 duct, and the other is the mechanical pressure upon the duct while it runs 

 over the frontal angle of the maxillary bone just before it reaches the base of 

 the fang. This mechanical compression is instantaneously removed as soon 

 as the fang is erected. 



