REPTILES. 



»nd into the intervals of the mufcular fafciculi compofiiig 

 tlie parietcs. From tliis ftrufturc it refults, that tliert- mull 

 be an admixture in the ventricle between the blood return- 

 intr from the lungs, and that portion which has not been 

 fiibmitted to the influence of the furrouiiding element in its 

 paffage through thofe organs. The opening between the 

 right auricle and the cavity of the ventricle is ni a fituation 

 immediately directed towards the two cavities leading to the 

 pulmonary arteries and arteries of the body ; they are both 

 fituated completely to the right, in the cavity of the ven- 

 tricle. Tlie lirlt, which is not always of the fame magni- 

 tude, is placed inferiorly to the other, having a wide com- 

 munication with it. In fome indajices the opening is ex- 

 tended very far towards the pofterior part of the heart ; in 

 others it is fo fmall, as in the land tortoifes, tiiat it does 

 not exceed the diameter of the cavity leading to it. It is 

 only in the firll conformation, of which we iind examples 

 in many of the fea tortoifes, that the appellation of pul- 

 monary cavity can be applied to it. Tlie blood arriving 

 from the right auricle purfues a direAion more particularly 

 towards that part, by a channel leading from the one to the 

 other. There is but one opening leadmg from the pul- 

 monary cavity, which is that of the pulmonary artery ; it 

 is provided with two valves, and penetrates the bate of the 

 heart more inwardly than the openings to be next men- 

 tioned. Thefe are the terminations of the two aortx, 

 which are found near to each other on the right fide of the 

 fuperior cavity, the fame which receives the blood of the 

 two auricles. The termination of the left aorta is fituated 

 a little more inwardly than that of the right, and inferiorly 

 to it. They are each provided with two iemicircular valves. 

 This is the ftrufture found in the fea tortoife ; but in the 

 land fpecies the arteries of the body arife by a lingle open- 

 ing from the ventricle. The heart of the turtle is beft de- 

 lineated by Mery, in the Acad, des Sciences, 1703. 



In the fecond order of reptiles, the faurians, we (hall 

 commence with a defcription of the heart of the crocodile, 

 which prefents an example of the mod complicated llruc- 

 ture that we have found in the animals of this order, or 

 even in the whole clafs of reptiles. The pericardium is 

 found, as in the chelonians, adhering to the peritoneum in- 

 vefting the convex furface of the liver. The apex of the 

 heart is connefted by a very llrong tendinous chord to the 

 loofe part of that bag, which is extremely thick, and has a 

 fibrous flrudlure externally. In its natural fituation the 

 organ is found occupying the fpace between the two lobes 

 of the liver and the lungs on each fide. The fize of the 

 auricles is fomewhat lefs than in the chelonians ; in other 

 refpet-ts they are fimilar. The parietes are flrengthened by 

 flefliy fafciculi proceeding in different direftions. The ven- 

 tricle prefents an oval form, and has its parietes of great 

 thicknefs. Its cavity is divided into three compartments, 

 sommunicating by numerous openings. One of thefe divi- 

 fions is fituated inferiorly and to the right. The auricle of 

 the fame fide projetts into its anterior part the blood re- 

 ceived from the veins of the body by a wide opening, which 

 is provided with two valves. The termination of the left 

 defcending aorta is found in the fame cavity, in its left and 

 anterior fide. Behind this latter opening is feen an orifice, 

 which leads into the fmalleft of the three divifions, at the mid- 

 dle of the bafe of the heart, and in which is found the com- 

 mon trunk of the pulmonary arteries. It refults from this 

 conformation, that there are two channels offered to the blood 

 which has palled from the right auricle into the cavity of 

 the fame fide ; the one by the left defcending aorta ; the 

 other into the cavity leading to the pulmonary artery. It 

 may even take a third route, and pafs through the numerous 



holes vviiich penetrate the partition feparating the fuperior 

 and Lft cavities. The left auricle projefts into the latter 

 the blood received from the pulmonary veins. A mem- 

 branous valve is found attached to the border of the open- 

 ing on its right fide. The trunk common to the right de- 

 fcending aorta, carotids, and axillary arteries, is fituate to 

 the right of the valve. The blood mull either pals into 

 the arterial trunk, ar.d from thence be dillributed to tlie 

 head and extremities, or penetrate into the intervals between 

 the flefhy fafciculi of that cavity, and from thence into tlie 

 two others. It refults from this llrudture, that the blood 

 diltributed to the anterior parts by the carotids and axillary 

 arteries, to the pofterior parts by the iliacs, and to the tail 

 by the middle facral artery, is nearly all derived immediately 

 from the lungs, whiHl a jjortion of that which is diftributed 

 to the other vifcera by the left aorta comes from the right 

 c.ivity and from the auricle of the fame fide, and confe- 

 quently has not been modified by its paflage through thofe 

 organs. The pulmonary blood is not fo intimately ad- 

 mixed with that from the body, as in the chelonians. Such 

 is the ftruAure of the heart in the crocodile of the Nile, 

 and the caiman or American alligator. For a view of the 

 crocodile's lieart, fee Cuvier Le9ons, t. 5. pi. 45. 



It is lefs complicated in the common iguana (iguana deH- 

 catifiima). In this animal, the fituation of the heart ig 

 very remote from the liver, beneath the origin of the lungs, 

 and in the molt projefting part of the cheft. It is of a 

 conical form, being very broad at its bafe, and acute at its 

 fummit. The auricles prefent nothing remarkable. In the 

 ventricle, there are but two cavities, the one fituate to the 

 right, which forms the proper cavity of the ventricle, the 

 other to the left and fuperiorly, appearing as a finus of the 

 former. The openings of the pulmonary auricle and right 

 defcending aorta are found in the latter, nearly in the fame 

 manner as in the crocodiles. The opening of the right au- 

 ricle is fituated towards the middle of the great cavity or 

 that of the ventricle, and is provided with a femilunar mem- 

 branous valve, in the fame way as that of the left auricle. 

 The orifices of the pulmonary artery and left defcending 

 aorta are placed lower down in the fame cavity ; the firft 

 on the left, the other on the right. There is no pulmo- 

 nary cavity. The interior of the ventricle is furnifhed with 

 fafciculi of flefhy fibres. 



The flrufture of the heart in the third order of reptiles, 

 the ophidians, differs but in a trifling degree from that of 

 the faurians, poireffing the moil fimple conformation ef this 

 organ. There is no diitinft pulmonary cavity. The auri- 

 cles are of confiderable fize ; that which receives the blood 

 from the body is the largeft. Their parietes are thin and 

 tranfparent in the intervals between the flefhy fafciculi, by 

 which their ftrength is augmented, and which are irregu- 

 larly interlaced together. Their cavities are feparated by 

 a membranous partition. The figure of the ventricle is 

 generally that of an elongated cone, irregularly formed in 

 confequence of an appendix of the fanne figure, which pro- 

 jefts from the left fide beyond its bafe. The interior is 

 divided into two cavities, the one fuperior, the other infe. 

 rior, the former being extended into the appendix. An 

 imperfeCl feptum intervenes between them, having a loofe 

 unconnefted edge on its right fide, and is extended hori- 

 zontally from the bafe to the apex ; it is compofed of flefhy 

 fafciculi, allowing the blood to penetrate in their intervals. 

 A confiderable opening, by which the two cavities commu. 

 nicate, is found towards the right fide of the bafe of the 

 ventricle, at the part where the feptum terminates. The 

 parietes of the ventricle, of themislves moderately thick, 

 afford attachment to a multitude of flelhy fibres, giving 



additiooal 



