686 EEPTILIA. 



comes within a distance of five or six inches from the Chameleon, the end 

 of this tongue is first slowly protruded to the distance of about an inch, 

 and then, with the rapidity of lightning, launched out with unerring 

 aim ; the fly, glued to its extremity, is with equal velocity conveyed into 

 the mouth. 



(1917.) The jaws of the Chelonian Reptiles are not armed with 

 teeth, but cased in horny coverings, so as to resemble the beak of a bird, 

 with which they crop the vegetable aliment upon which they generally 

 subsist. 



(1918.) Serpents, as regards their means of destroying prey, may 

 be divided into two great groups the first including those which are 

 not venomous, the second embracing such as are armed with poison- 

 teeth. 



(1919.) 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, veiy sharp, and point backwards. Each divi- 

 sion 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 in- 

 tended for a very different office. These serpents kill their victims by 

 coiling their lengthy bodies around the chest, and then by strong mus- 

 cular contraction they compress the thorax of their prey so firmly, that, 

 its movements being completely prevented, respiration is put a stop to, 

 and the animal so seized speedily perishes from suffocation. But, having 

 succeeded in extinguishing life, the most difficult task still remains 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 in- 

 ferior maxilla become 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 were 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 muscles 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 converted into a sort of valve : pointing 

 backwards, as they all do, they permit the bulky food to pass into the 

 fauces ; but at tho same time their sharp points, being directed towards 



