REPTILIA. 557 



Serpents, as regards their means of destroying prey, may be di- 

 vided into two great groups ; the first including those which are not 

 venomous, the second embracing such as are armed with poison-teeth. 



(614.) In the non-venomous serpents, as for example in the 

 Boa constrictor, the upper jaws and the palate-bones are all lined 

 with sharp teeth, so that there are four rows of dental organs, two 

 placed along the margins of the maxilla, and two projecting from 

 the roof of the mouth : all these teeth are simple, very sharp, and 

 point backwards. Each division of the lower jaw is likewise armed 

 with a single row, which are also directed towards the back of the 

 mouth. It must be evident, from a mere inspection of these teeth, 

 that they can be of little use in holding, much less in destroying, 

 such strong and large animals as the Boa devours ; and upon a little 

 consideration we shall find that they are intended for a very diffe- 

 rent office. These serpents kill their victims by coiling their lengthy 

 bodies around the chest, and then by strong muscular contraction 

 they compress the thorax of their prey so firmly, that, its move- 

 ments being completely prevented, respiration is put a stop to, and 

 the animal so seized speedily perishes from suffocation. But, hav- 

 ing succeeded in extinguishing life, the most difficult task still re- 

 mains to be accomplished : how is the serpent, utterly destitute 

 as it is of all external limbs, to force down its throat the carcase of 

 a creature many times thicker than its own body ? The mode 

 adopted is as follows : Once more winding itself around the 

 slain animal, it commences at the head, which by main force it 

 thrusts into its mouth ; the elastic ligament at the symphysis of its 

 lower jaw gives way, and the branches of the inferior maxilla be- 

 come widely separated, so that the mouth is stretched enormously 

 as the food is thus forced into it. Deglutition is here a very 

 lengthy and laborious process ; and, was there not some special con- 

 trivance to guard against such an accident, no sooner were the 

 efforts of the snake relaxed in the slightest degree, than the mus- 

 cles of the throat and jaws, being in a state of extreme tension, 

 would force out of the mouth what had already been partially 

 swallowed. To provide against this, the teeth are in this case con- 

 verted into a sort of valve : pointing backwards as they all do, they 

 permit the bulky food to pass into the fauces, but at the same time, 

 their sharp points being directed towards the throat, efficiently pre- 

 vent it from being pushed back again in the opposite direction.* 



* In the collection of Professor Bell there is a small snake, which having by mis- 

 hap attempted to swallow a mouse of too large size, and being quite unable, in conse- 



