646 



CIRCULATION. 



heart (A, H ) receives the whole venous blood 

 of the body by the right auricle, and a small 

 quantity of arterial blood from the lungs by 

 the left. These two kinds of blood, mixed 

 together in the common ventricle, proceed 

 from thence into the aortic bulb and its 

 branches (A, B, b}. In the larva of the Sala- 

 mander and Protean Reptiles, a part of the 

 blood is sent by pulmonary vessels to the 

 lungs, from which it is returned by the pul- 

 monary veins to the heart ; a part passes di- 

 rectly round the arches, and gains the descend- 

 ing aorta ; the greatest quantity passes out into 

 the gills, and after being arterialized returns to 

 be mixed with that in the aorta, so that a 

 mixed blood must permeate all the vessels of 

 the systemic circulation. In the Siren, accord- 

 ing to Cuvier and Owen, the whole blood goes 

 at once to the gills, from the want of any com- 

 municating twigs across the root of these 

 organs. It is interesting to remark that the 

 arteries of the head and upper extremities (a) 

 are not given off by the aortic arches until 

 after they are joined by the returning branchial 

 vessels, a disposition which is in some respect 

 similar to what we find in higher Reptiles, and 

 which seems to have for its object the supply 

 of a more pure arterial blood to the cerebral 

 organ. 



In the larva of the Frog, the course of the 

 blood is very similar to that of Fishes. The 

 whole of the venous blood propelled through 

 the heart is sent into the gills, and is made to 

 pass through them before reaching any other 

 part. From the posterior parts of the first 

 arches are given off the vessels of the head, the 

 second form the right and left roots of the de- 

 scending aorta, and the fourth are continued 

 upon the lungs in the form of a pulmonary 

 artery. There is however also in the larva of 

 the Frog a short anastomosis between the out- 

 going and returning artery of each of the gills, 

 which allows of a direct passage of some blood 

 round the arches of the aorta. 



In the Protean Reptiles and larva of the 

 Batrachia a greater quantity of blood is sent to 

 the respiratory organ than occurs in the adult 

 Frog or Salamander. 



Portal circulation in Reptiles. In the class 

 of Reptiles there are two lesser venous circula- 

 tions besides those already described ; the one, 

 similar to the portal circulation of warm-blooded 

 animals, belongs to the liver; the other, which 

 does not appear to occur either in Birds or 

 Mammalia, belongs to the kidneys. According 

 to Jacobson, who was the rst to point out the 

 existence of veins carrying blood to the kidneys 

 in the Amphibia, and the later researches of 

 Nicolai and others, there are two principal ves- 

 sels which carry back blood from the posterior 

 parts of the body, viz. the anterior abdominal, 

 and the inferior renal veins. These two vessels 

 are formed by the union of the iliac, caudal, 

 posterior cutaneous, pelvic, visceral, abdominal, 

 and umbilical veins; and in most Reptiles, ex- 

 cepting the Ophidia, the renal and portal vessels 

 proceeding from the posterior parts of the body 

 arise together. In some Reptiles the whole of 

 the blood returning from the posterior parts of 



the body is divided between the portal veins of 

 the liver, and the venae advehentes of the kidney ; 

 in others a part is also sent into the abdominal 

 vena cava. The inferior renal or advehent 

 veins of the kidneys (Jigs. 316, 317, and 318, 

 jfiC) carry venous blood to these organs, and 

 distribute it minutely through their substance. 

 It is removed from thence and returned into 

 the great circulation by the revehent or superior 

 renal veins (/c) which lead into the vena cava.* 

 The anterior abdominal vein (fig. 316, u) is the 

 same to which Bojanus has given the name of 

 umbilical in the Tortoise, in which class of ani- 

 mals it is of very large dimensions, and receives 

 not only the venous blood from the posterior 

 extremities and shell, but also some from the 

 anterior extremities. The persistence of those 

 umbilical veins which proceed from the large 

 urinary bladder in many of the adult reptiles is 

 a fact of some interest, because it points out a 

 resemblance between the permanent distribu- 

 tion of the vessels in these reptiles and the 

 foetal condition which we find in the higher 

 animals, and likens the bladder of the scaly 

 Reptiles, as well as of the Batrachia in which 

 during foetal life no allantoid membrane is ever 

 formed, rather to an allantoid receptacle than 

 to a proper urinary bladder. 



Fishes. In fishes there is no vestige of a 

 pulmonary organ, and the respiration is wholly 

 effected by means of the gills. The branchial 

 apparatus of fishes is internal or covered, like 

 that of the larva of the frog ; it is placed on 

 the cervical part of the alimentary canal, and 

 is formed by the fine subdivisions of aortic 

 arches (Jig. 319, A, B, b}, which are prolonged 

 into the fringed or leafy processes of the hyoid 

 branchial arches. The respiratory organ is 

 thus placed in this class in the course of the 

 arterial circulation. The venous blood from 

 . the body generally, and from the liver, enters 

 the single auricle (A) through the great sinus 

 (V), and is wholly propelled into the arterial 

 bulb by (A) the single ventricular cavity (H). 

 No systemic arteries come from the aortic bulb, 

 but this vessel carries by the arches into which 

 it divides (B), the whole of the venous blood 

 into the gills. The number of these arches 

 subdividing and ramifying in the gills varies 

 in different fishes. In a few, as the Lophius, 

 there are only three on each side. In most 

 osseous fishes there are four. In the Skates 

 and Sharks there are five. In the Lampreys 

 there is the greatest number known, namely, 

 six or seven. 



The blood, after having undergone arteria- 

 lization in the gills, is not returned to the heart, 

 but proceeds directly through the branches of 

 the aorta (j^g.319*, b 6, A) to different organs. 

 The force of the heart acts therefore through the 

 whole of the capillary system of the gills (be ), 

 and continues to propel the arterialized blood 



* It must be remarked that Meckel, who appears 

 to have examined the distribution of the above men- 

 tioned vessels with great care, denies entirely the 

 advehent function of the lower veins of the kidneys 

 both in fishes and reptiles, considering all the veins 

 of the kidney as revehent. Vergleich. Anat. B.V. 

 S. 201 and 253. 



