BOA. 



537 



This mouth, therefore, not only differs from but is 

 in a great measure the very* reverse of those mouths 

 with which we are familiar in ordinary animals. In 

 these the power of the mouth is in shutting the jaws 

 against each other ; arid whether the teeth be fitted 

 for tearing, for cutting, for grinding, or for simple 

 prehension (as they are in most fishes^, the efficiency 

 of the animal, and the danger, if it is a powerful and 

 rapacious one, are in the bite. The snakes, or harm- 

 less serpents, which have in the form of their skele- 

 tons some ruditnental resemblance to the saurian 

 reptiles, have the mouth, though rather loose in its 

 articulation, constructed in a manner similar to the 

 rest of the vertebrated animals ; and, therefore, its 

 most powerful action is in the bite, though that bite 

 is, from the looseness of the articulation, very feeble, 

 which is the reason that the animals are so very 

 harmless. 



Of the true serpents, those which have poison 

 fangs, have not in general the gape so capable of ex- 

 tension as the boas and others which are without 

 poison apparatus ; but, even in these it is dilatable to 

 a degree quite; unknown among any other animals, 

 and quite sufficient to rank them in the same sub- 

 order with the crushing serpents. 



In these, the jaws have their greatest action in 

 opening. The sides of the gape, as they appear 

 when the mouth is closed, are not only brought into 

 one plane, but the junction of both jaw-bones in front 

 and that of the lower ones, or rather of the interme- 

 diate bones, with the cranium behind, are greatly ex- 

 tended ; so that the entire circumference to which 

 the mouth opens as a swallowing organ is much 

 greater than the measure round both jaws to the 

 extremity of the gape when shut. A fox trap, or a 

 purse which opens by a circular strap, the two sides 

 or valves of which ibid completely back from each 

 other till they are in the same plane, will afford an 

 approximate notion of this formidable gape. But it 

 is only au approximation, for the stretching of the 

 ligaments which connect the different bones can, 

 upon occasion, double the opening made by the bones 

 themselves. Bringing the gape to this state is a 

 work of some time with the animal, and it seems to 

 excite the muscular part of the body at the same 

 time ; for the moment that the mouth is opened to 

 the requisite extent, the snake darts on its prey. The 

 teeth in both jaws, though not biting teeth, or capable 

 of inflicting any deadly or even serious wound, aie 

 recurved, so that they assist powerfully in the act ol 

 swallowing whatever the great gape can admit. 

 Figures and even stuffed specimens of these snakes 

 are sometimes represented as biting at the throats o: 

 those animals round which their folds are coiled; but 

 this would be a very unnecessary operation to them 

 as it could in no way facilitate their purpose, which 

 is to swallow the animal entire. If the animal is 

 large, the crush of the folds is sufficient to kill it 

 ami if it is small, even that is not necessary, as it is 

 taken into the mouth at once a gulf from which 

 there is no return. 



The smearing with the slimy saliva tends to make 

 the prey slide more easily into the gullet, which di- 

 lates to receive it to the same extent as the opening 

 of the mouth. The form of the teeth and the pecu- 

 liar junction of the jawbones, in consequence of which 

 they can act either all at the same time or by turn? 

 urges the prey inward, something in the same manner 

 as the awn or beard of a barley-corn moves up a 



man's sleeve when he moves his arm, or as hairs work 

 nto a compact mass in the operation of making a hat, 

 or any other process of felting. 



It does not appear that any of these serpents break, 

 or have the power of breaking the skull of their prey ; 

 jecause a case of bone of the form of a skull is very 

 difficult to break by compression all round it. The 

 jape is therefore adapted to admit the head of the 

 animal, and then the rest follows as a matter of 

 course. 



The quality of the slimy matter with which the 

 Hey is covered has not been examined ; but it is not 

 mprobable that it has a solvent as well as a smoothing 

 power, and assists in digestion as well as in degluti- 

 :ion. At all events the work of decomposition in the 

 prey soon begins ; and as there can be little except 

 solvent action exerted upon it, that action must .be 

 very powerful, and it constantly goes on along the 

 whole canal from the month till the prey is com- 

 pletely reduced to matter tit for the nourishment of 

 the reptile. 



When we consider this wonderful mode of feeding, 

 we need hardly wonder at the stupor which ensues ; 

 for, what with the dilatation of the mouth and gullet, 

 what with the action of the jaws and teeth in "work- 

 ing in" the prey, to say nothing of the vast muscular 

 effort requisite in crushing to death an animal, round 

 which the serpent's coils appear not much thicker 

 than those of a cable round a mast, the feeding of 

 one of these crushing serpents is among the most 

 laborious operations which we know of, or can 

 imagine, in the whole range of animated nature. And 

 though there certainly is nothing pleasing in the 

 study of these singular creatures, they form one of the 

 most remarkable, and far from one of the least in- 

 structive studies that we meet with in the whole 

 compass of natural history. 



We have entered so much into the general struc- 

 ture and action of these reptiles, that we shall be 

 enabled to dispose of the different species very briefly. 

 Cuvier makes five divisions of them, besides the allied 

 subgenera, which have more resemblance to the boas 

 than to any other genus of serpents. 



The first are those which "have the head, to the 

 point of the muzzle, covered with small scales, the 

 same as those on the body ; and the scaly or horny 

 plates on the jaws are not grooved or dimpled. To 

 this division belongs Boa Constrictor, the "roebuck 

 serpent," one of the largest and most formidable of 

 the genus. It is easily known by the markings along 

 the back, which are very distinct. These consist of 

 a regular succession of spots, the whole length of the 

 mesial line, alternately black, and in the form of irre- 

 gular hexagons, and ovals of a yellow colour, and 

 broken by notches at the sides. The annexed figure 

 will give a general idea of this powerful reptile. 



It has sometimes been supposed that the boa con- 

 strictor exists in the old continent, in the hottest 

 parts of Asia and Africa, and there only ; but, as has 

 been mentioned, the probability is that the large 

 serpents found in those places are colubers, and that 

 the true boa constrictor, answering to the generic 

 description, is found only in the richer parts of 

 tropical America. 



A second section of the genus have scaly plates 

 behind the eyes, as well as on the sides of the jaws and 

 front, of the muzzle, by which they are easily distin- 

 guished from the former section, though, like that, 

 they have no dimples or furrows on the jaws. They 



