ORGANS OF CIRCULATION. 



19s 



the caudal and subintestinal veins 

 is lost. Modifications now set up 

 in the capillary system of the meso- 

 nephros not easily described in a 

 few words, but readily made out 

 from Fig. 205, the result being 

 that the interrenal part of the cau- 

 dal vein becomes continuous with 

 both posterior cardinals, while the 

 posterior portion of the caudal vein 

 divides and extends forwards upon 

 the lateral sides of the Wolffian 

 bodies, absorbing the posterior 

 part of the posterior cardinals, and 

 with them receiving the blood 

 from the posterior appendages.^ 



In front of the kidneys in elas- 

 mobranchs, the posterior cardinals 

 meet and fuse in the median line, 

 thus forming a cardinal sinus be- 

 tween the gonads. In the teleosts 

 the cardinals unite behind with the 

 caudal vein, and then that of the 

 left side closes near the middle, so 

 that the blood from the left kidney 

 usually passes backwards to enter 

 the right cardinal on its way to the 

 heart. 



In the dipnoi and amphibia a 

 new vein, the postcava (vena cava 

 inferior), comes into relations with 

 the system just described. It be- 

 gins as an outgrowth of the right 

 hepatic vein, and extends back and 

 joins the right posterior cardinal 

 just in front of the Wolffian body, 

 so that now a large part of the renal 



Fig. 206. Diagram of the 

 venous system of an Amphibian, 

 w, auricle ; aa, anterior abdominal 

 vein ; c, caudal vein ; dc, ductus 

 Cuvierii ; h, hepatic vein ; ;', iliac 

 vein; zV, interrenal vein ; y, jugu- 

 lar'; Ic^ left cardinal; w, meso- 

 nephros; p, portal vein; pc, 

 postcava ; re, right cardinal ; s, 

 sinus venosus; v, ventricle. 



1 This has been greatly abbreviated in mammals. 



