330 



THE RISE OF ANIMAL LIFE 



Fig. 13-50. This is a series of photos showing a 

 common garter snake swallowing a frog. It wil- 

 lingly attacks a large leopard frog but after get- 

 ting one leg rather well swallowed and being 

 confronted with the remainder of the animal, it 

 apparently saw the futility of its efforts and re- 

 leased its prey shortly after this picture was taken 

 (top left). It then tackled a smaller frog and this 

 time started swallowing its prey head first, which 

 proved to be quite satisfactory as the next three 

 pictures indicate. Note how the expansible jaws 

 accommodate the frog, which is twice the diam- 

 eter of the snake's head. 



fact that the lower jaw articulates with the 

 skull very loosely by means of two slender 

 bones; furthermore, the lower jaw can 

 spread at tlie anterior midpoint, allowing 

 a lateral expansion ( Fig. 13-49 ) . With such 

 a loose jaw arrangement, it is possible for 

 the snake to spread its mouth to an extraor- 

 dinary degree (Fig. 13-50). 



The snakes have received their bad repu- 

 tation from the poisonous members of the 

 group. Just how these creatures evolved 

 this deadly offensive and defensive mech- 

 anism is hard to say. Many different kinds 

 of tooth formations have been produced for 

 inoculating the poison into the wound 

 made by the sharp teeth. In some forms, 

 such as the rattlesnake, the fangs possess 

 a hollow tube through which the venom is 



injected, as with a hypodermic needle ( Fig. 

 13-49). Others, such as the cobra, have 

 deep-grooved fangs which allow the poison 

 to enter at the base of the tooth and exit 

 near the tip so that, upon striking, it would 

 be deep within the wound. The poison 

 glands are located above the angle of the 

 jaw and empty their venom into a flap of 

 skin at the base of the fangs (Fig. 13-48). 

 Normally the fangs lie against the roof of 

 the mouth pointing down the throat, but 

 when the head is thrown back they are 

 forced forward until they protrude at right 

 angles to the roof of the mouth. The head is 

 then thrown forward with a sudden lunge, 

 about two-thirds the length of the animal, 

 striking the prey and penetrating the skin. 

 The compression of the victim's skin against 



