BOA CONSTRICTOR. 293 



FAMILY III. BOAS. 



The family of Boas (Boidce) contains a considerable number 

 of species, upwards of forty being described in the catalogue of 

 the British Museum. They are, generally speaking, the largest of 

 all the Serpent tribe, and are characterized by several distinctive 

 marks. The greater number of them have a prehensile tail, which, 

 though short, is excellently fitted for grasping the branches of 

 trees. They possess rudimentary hind extremities, which are de- 

 veloped under the skin. These consist of several small bones, 



FIG. 317. VENT A:;D HOOK CF BOA. 



terminated by a horny spur not unlike the spur of a fowl in 

 miniature : these little claws project externally a little in front of 

 the vent (Fig. 317). Their body is well adapted for twisting and 

 twining round other objects, and the scales that cover it are small 

 and numerous. 



The Boa Constrictor has the upper jaws and palate-bones lined with teeth, all 

 of which are very sharp and pointed backwards. Each side of the lower jaw is likewise 

 armed with teeth, all directed towards the throat. It must be evident, from a mere in- 

 spection of these teeth, that they can be of little use in holding, much less in destroy- 

 ing, such strong and large animals as the Boa devours, and upon a little reflection we 

 shall find that they are intended for a very different purpose. These serpents are said 

 to watch in the forests, and especially near the drinking-places of rivers there, hanging 

 from a tree, until some quadruped passes within range. On its approach, the Boa darts 

 upon its prey, and, more swiftly than the eye can follow, encircles it in voluminous 

 folds. The Boa thus kills its victims by coiling its lengthy body round their chest, ami 

 then, by strong muscular contraction, compressing the ribs so firmly that respiration 

 is prevented, 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 an animal many times thicker than its own body ? The mode adopted is as 

 follows : Having relaxed the dreadful embrace, it once more winds itself round the 

 slain animal, and commences with the head, which, by main force, it thrusts into its 

 mouth the jaws becoming widely separated, so that the throat is stretched enormously 

 as the food is forced into it. Deglutition is here a very lengthy and laborious process, 

 and was there not some special contrivance to guard against such an accident, no sooner 

 were the efforts of the snake relaxed in the slightest degree, than the muscles of the 



