318 POISONOUS SNAKES 



As the fangs are directed backward it is necessary for the snake when striking 

 to open widely the jaws and bend back the neck. The fangs are then brought 

 forward and erected by the spheno-pterygoid muscles. The snake bite is a com- 

 bination of bite and blow. The functional fangs of colubrine snakes however are 

 not mobile. 



In addition to the possession of the pit, these vipers have a more or less trian- 

 gular head and in particular a single row of large scales on the under surface posterior 

 to the vent (anus) , while the harmless snakes show an elongated oval head and two 

 rows of large ventral scales posterior to the vent. 



FIG. 96. i, Single row of scales posterior to vent (poisonous snakes water 

 moccasin); 2, double row scales of harmless snake (Natrix); 3 and 5, side and dorsal 

 view of head of pit viper; 4 and 6, side and dorsal view of head of harmless snake 

 (Natrix) ; 7 and 9, bite puncture and skull of Elaps; 8 and 10, bite puncture and skull 

 of harmless snake. 



In examining the wound made by a snake the two punctures of the 

 fangs indicate the bite of a poisonous snake. If these fang puncture 

 points are far apart it shows that a large snake, and probably one 

 capable of injecting a greater amount of venom has given the bite. 



When a snake strikes the fangs move from the horizontal to the erect position, 

 the mouth being widely open. When the fangs enter the jaws close and pressure 

 is exerted on the poison glands so that the venom pours out. 



The amount of venom varies with the size and condition of the snake, an adult 

 cobra yielding about i c.c. 



