532 



REPTILE. 



smaller than either of the other two ; it is this left 

 compartment which receives the blood back again 

 from the pulmonary veins ; there is thus a very com- 

 plicated circulation in the crocodile that toward the 

 anterior part of the body approximating the circulation 

 of the mammalia, and that toward the posterior part 

 being more completely the circulation of a reptile ; 

 we may therefore suppose that the fore part of the 

 crocodile, is more constantly in readiness for action 

 than that of any other reptile, and this is confirmed 

 by the power and energy with which the animal uses 

 the jaws instantly, and from a previous state of per- 

 fect stillness and repose. As the hind part of the 

 animal does not take much share in this ready energy, 

 it follows the general law of reptiles. The motion of 

 the animal is but slow, and whether in the water or 

 on the land it never takes its prey by chase, but 

 always by lying in wait, and in most cases in the 

 water only. The Satiria, which live mostly on the 

 land, and are nimble-foote'd, have not this circulation 

 in the two ends of their bodies ; but the examination 

 of the greater part of them has been so imperfectly 

 made, that it is not easy to trace, in a satisfactory 

 manner, the relation between the circulation and the 

 activity of the animals. This is much to be regretted, 

 and it were earnestly to be desired that able and 

 uiihypothesis-bitten physiologists would direct their 

 best attention to the working of the system in rep- 

 tiles ; for, from the peculiar way in which they are 

 situated on the confines, as between class and class, 

 it is highly probable that they would help us more to 

 a rational understanding of the highly interesting but 

 very serious subject of animal life, than any of those 

 classes which have their locality fixed and definite. 



In the frogs and other batrachian reptiles the cir- 

 culation is very simple. The heart in these consists 

 of only two cavities, one auricle and one ventricle ; 

 it does not therefore appear that they are capable of 

 working themselves up to any degree of energy at all 

 comparable with that of those orders which have the 

 heart of more complicated structure ; and as they 

 have the aquatic structure, or breathe by means of 

 gills, in the early stage of their being, they appear to 

 retain a portion of this character through life ; and 

 hence many of them which are upon the land occa- 

 sionally, in the warm season, take up their winter 

 abode and pass into the dormant state in the water. 



The other branch of this division of the subject is 

 the breathing apparatus. In those reptiles that live 

 and breathe in the water when young, and also in 

 the very few and obscure species which retain this 

 power of breathing along with that of breathing in the 

 air, and which are therefore the only true amphibia 

 in the animal kingdom, the gills resemble those of 

 fishes in their structure ; they consist of a number of 

 filaments around which the water can play, and this 

 appears to be the only form of an apparatus by means 

 of which an animal can breathe air through the resi- 

 duum of water. Between these and the gills of fish 

 there is, however, a very remarkable difference in the 

 adaptation ; the bone fishes have lids and flaps by 

 means of which they can work their gills; and even 

 the cartilaginous fishes that have fixed gills, have them 

 in sacs or cavities, which have the power of alternately 

 expanding to receive the water, and contracting to 

 reject it after it has done its office. The gills of the 

 reptiles, whether young or mature, have, on the other 

 hand, no accompanying apparatus by means of which 

 the animal can work them. They are placed on the 



sides of the neck without any apparatus or covering 

 whatever, and then the animal cannot work them by 

 any effort on its part ; hence those reptiles which 

 retain them through life are among the most dull of 

 all known animals, and are among the very lowest 

 types of the vertebrated form. 



The lungs of reptiles resemble those of the other 

 vertebrated animals in their general strutuie that 

 is to say, they are composed of cells into which air 

 may be admitted, and from which it may be again 

 expelled ; but in respect of structure, and of the 

 means of working that structure, they are far inferior 

 to those of the mammalia and the birds. They are 

 in general larger in their whole volume, and extend 

 farther down into the abdominal cavity, but they are 

 lesser in their texture ; their cells are much larger ; 

 they do not, bulk for bulk, expose nearly so much 

 surface to the air ; they are much less elastic in their 

 own structure, and the apparatus lor working them 

 are exceedingly imperfect. In the tortoise they are 

 of uniform structure, but the cells are large and few, 

 and the walls or partitions between them comparatively 

 loose and flaccid. In the Sanrin the lungs, which are 

 in two lobes, one on each side of the heart, there is a 

 sort of double division, or rather division and sub- 

 division, into cells first they are divided into poly- 

 gons by large partitions, and then into cells by 

 smaller ones ; but in most cases also these cells have 

 not much elasticity in their walls, and the smaller 

 ones are much larger than the cells in the lungs of 

 mammalia. The lungs of the Batrackia resemble those 

 of the Sanria, but they are still more simple, consist- 

 ing of fewer cells ; and they are not developed until 

 the metamorphosis in which the gills are lost or ab- 

 sorbed, these lungs float loosely in the cavity, and, 

 as already hinted, they are in all cases much less 

 elastic than the lungs of other animals. The air can 

 thus much more easily distend them, and thus the 

 animals can inhale a large quantity, or rather passively 

 receive it. In consequence of this, as well as of the 

 less need they have for air, the breathing in reptiles is 

 very slow, and particularly so when they sleep. It 

 appears indeed that, in very many of them, the tran- 

 sition from sleep to perfect dormancy is short and 

 easy. The common turtle will live for four or five 

 weeks, though the mouth and nostrils are both effec- 

 tually closed. Reptiles will also live much longer 

 than the other vertebrata in the same quantity of 

 atmospheric air, but they will not live in air which is 

 wholly deprived of its oxygen. In what may be called 

 the voluntary taking in of air, which the reptiles, from 

 their capability of suspending their respiration, ne- 

 cessarily possess in a higher degree than those ani- 

 mals which cannot suspend it long, they do not draw 

 it in by the action of the chest and diaphragm 

 like the mammalia ; they drink it, that is, they 

 take it into the mouth and gulp it down by the 

 action of the throat, much in the same way as a car- 

 nivorous animal gulps down water. The chelonians 

 make way for it by raising the shield at the back 

 part, and depressing the breast-plate at the same ; 

 the first being accomplished by the mere relaxation 

 of the muscles at that part, and the last by the con- 

 traction of the same. In short, the two plates work 

 something in the same manner as the boards of a 

 common pair of bellows, only they work slowly and 

 to a very limited extent. The respiration in the 

 Snuna is performed by the action of the ribs, tha ab- 

 dominal muscles, and the tendinous continuations i( 



