308 



REPTILIA. 



the right side of the heart, a branch ascending 

 from the division to form the axillary and 

 carotid arteries; whilst the two great lateral 

 trunks bend outwards right and left ; the left, 

 after giving off some branches to the intesti- 

 nal canal and liver, unites on the vertebral 

 column with the right and larger branch, form- 

 ing with it the descending aorta which sup- 

 plies the other parts of the body, a vascular 

 circle being thus produced precisely as in the 

 frog. A second circle, as has been proved by 

 the observations of Meckel and Munniks, is 

 formed by the pulmonary artery, which, like 

 the aorta, is furnished with two semilunar 

 valves, and immediately after its origin divides 

 into a right and left branch, each of which enters 

 one of the lungs ; but, at the same time, commu- 

 nicates with the corresponding branch of the 

 aorta by means of an arterial canal (ductus Bo- 

 talli), which, probably, is permanently pervious. 

 As a consequence of these dispositions, but a 

 small part of the blood is exposed to the 

 action of the atmosphere, and the oxidation 

 of the blood would be even less perfect than 

 in fishes, where all the blood passes through 

 the gills ; were it not that in the latter the 

 respiration is merely of water, and that pro- 

 bably in these and other amphibia there is, in 

 addition to the pulmonary respiration, a res- 

 piration of an aqueous kind performed by the 

 permanently existing allantois. As to the 

 veins, it is remarkable that here, according to 

 the investigations of Bojanus, the blood of the 

 whole posterior part of the body, the abdo- 

 minal coverings, posterior extremities, &c. 

 (with the exception of the venous trunk 

 belonging to the kidneys and sexual organs), 

 is carried into the liver by two trunks, in 

 order to circulate partly in this organ, and 

 partly, according to Jacobson, by means of 

 inferior renal veins in the kidneys, previous to 

 arriving at the heart, The venous blood 

 of the body, as well as that of the lungs, 

 is collected into a venous receptacle for each, 

 close to the auricles, which it then enters in 

 the manner already described. 



In serpents, the heart is situated towards 

 the middle line of the body, in front of the 

 lungs, and above the liver. Here, also, it is 

 furnished with a left pulmonary auricle, and a 

 right systemic one, which is nearly as large 

 again as the former; both open into the 

 simple and fleshy oblong ventricle, from 

 which arises a double aorta, the branches 

 of which meet again on the vertebral column. 

 The pulmonary artery is single in those ser- 

 pents where the lung is single. 



In lizards, the structure of the heart offers 

 a great similarity to that of tortoises, consisting 

 of two separate auricles, and a single ventricle, 

 which, however, is generally divided into seve- 

 ral cells. In several species, e. g. the croco- 

 dile, the heart is attached by a tendinous 

 ligament to the pericardium. The situation of 

 the heart is here again usually immediately 

 above the liver ; though, according to Cuvier, 

 in the iguana, at a considerable distance 

 from it, and quite in the front part of the 

 thorax, Its auricles are proportionately 



smaller than in tortoises, and separated by a 

 thin septum, which is perforated in the La- 

 certa apoda. The ventricle, the form of which 

 is tolerably similar to those ofr the human 

 heart, is divided, in the crocodile, into three 

 anastomosing cells, in such a manner that the 

 blood of the venae cavae passes from the right 

 auricle into the two inferior cells on the right 

 side, from which the pulmonary artery and 

 left ascending aorta arise ; whilst, on the 

 contrary, the pulmonary venous blood flows 

 from the left auricle into the left superior 

 cell, which is more distinct from the other 

 two, and which gives origin to the right 

 aortal, carotid, and axillary trunks : the latter 

 vessels, consequently, are not only filled by 

 blood that is more oxidised than "that of the 

 left aorta, but also contains a smaller propor- 

 tion of venous blood than the arteries of the 

 tortoise, inasmuch as but little blood penetrates 

 this from the other two cells. 



According to Mr. N. M. Hentz, the 

 American alligator (Crocodilus luciits) pre- 

 sents a much more perfect structure of the 

 heart than any other of the reptilia, the two 

 ventricles not having any immediate com- 

 munication. From his description the fol- 

 lowing particulars are derived. The vena 

 cava superior follows the course of the right 

 subclavian artery in its passage through the 

 chest, and descends to the pericardium to 

 join the vena cava inferior opposite the right 

 auricle. In its course upwards, the inferior 

 cava runs upon the right side of the spine 

 until it reaches a straight channel in the 

 substance and near the edge of the liver, 

 where it receives four or five venae cavas 

 hepaticae. A vein analogous to the right 

 subclavian enters the upper part of the right 

 auricle at its left side. The auriculo-ven- 

 tricular opening of the right heart is furnished 

 with two valves. The right ventricle opens 

 into two arterial tubes, of which or>e is the 

 pulmonary artery ; the other, at the left and 

 upper part of the ventricle, is furnished at its 

 base with two semilunar valves, and termi- 

 nates in the left aorta. There is not any 

 direct communication between the cavities of 

 the two ventricles. The left ventricle, which 

 is rather smaller than the right, and situated 

 behind and somewhat above it, has also two 

 valves at the orifice by which it communicates 

 with the auricle. Like the right ventricle, 

 also, it opens into two arterial tubes, of 

 which the first leads into the left aorta, and 

 is separated from the corresponding orifice of 

 the right ventricle by a cartilaginous septum 

 only. It is important to observe that, this 

 septum interrupts the immediate communi- 

 cation between the cavities of the two ven- 

 tricles (for they communicate intermediately 

 by means of the artery from each opening 

 into the left aorta), and constitutes the most 

 essential variation of the structure of the 

 heart in this, from what is found in other 

 Saurians. This first branch, arising from 

 the left ventricle, is bordered by a valve 

 at its origin that nearly closes its cavity. 

 The second artery from the left heart divides 



