POISON APPARATUS OF VENOMOUS SNAKES 69 
The whoie 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. 
