308 ANNTJAL REPORT SMITHSONIAN INSTITUTION, 1951 



Defenseless snakes, burrowers and tree-climbers, on the other hand, 

 are usually slender and built for speed. The record is probably held 

 by the American black racer {Coluber constrictor)^ which is said to 

 attain the speed of a running man. 



The fastest of all snake movements, however, may be claimed by 

 the vipers. Otherwise sluggish, and apt to stand their ground when 

 attacked, they stri}s:e at lightning speed. When time permits, the 

 rattlesnake or viper will coil the forequarters into the shape of a 

 watch spring with the head in the center. This can then be shot 

 forward for about a third, even a half, the length of the body to 

 produce one of the fastest movements in the reptile world. Only a 

 few animals, such as the mongoose and some birds, are able to avoid 

 it, and even these are not always quick enough to avoid the strike 

 (pi. 1, fig. 2). 



This brings us to another part of the snake's unique machinery, 

 the jaws. In birds and mammals, man included, there is only one 

 articulation of the skull bones, the point at which the lower jaw 

 hinges onto the cranium. In a snake's skull the bones of the jaws 

 function as prehensile organs and do not masticate the food. They 

 are attached to one another and to the cranium by elastic ligamentous 

 tissue, which permits much distortion and wide expansion of the 

 mouth. This, together with the expansion of ribs and body wall, 

 allows for the passage of a prey that far exceeds in cross section the 

 size of the head. 



The focal point of the jaw action is at the point where, at the 

 back of the skull, the two bones called the quadrate and pterygoid 

 meet the lower jaw (see pi. 2). As the quadrate bone is levered for- 

 ward by muscle action a thrust is transmitted to both the upper 

 and lower series of jawbones which possess teeth. These slide over 

 the meal, hooking on farther forward as the prey is worked down 

 the gullet. The most noticeable movement is in the lower jaw, the 

 two halves of which can separate widely at the tips, where normally 

 they are held in place by elastic ligament. This allows for enormous 

 expansion of a mouth with normally wide gape that extends to well 

 beyond the eyes. 



Each half of the jaw has independent movement and is pushed 

 forward alternately to its neighbor in a chewing action as the owner 

 literally pulls itself over its prey. A copious flow of saliva in the 

 mouth helps to lubricate the passage of the prey along the gullet. 

 It is a slow and laborious proces-s, painful to watch. Once the prey 

 is past the teeth, swallowing is speeded up as the muscles in the body 

 wall take over, and the meal travels as a visible bulge into the stom- 

 ach. Prey of large size is usually swallowed head first. By the 

 mechanized means described above, which is peculiar to snakes, a 



