320 



FISHES 



CHAP. 



1 .^^.z; 



forwards along the outer border of the kidney of its side, it re- 

 ceives a number of segmental veins, and, at the same time, gives 

 off branches to the renal capillaries. In addition, each renal 

 portal vein is connected with the hepatic portal vein by a series 



of singular arch-like vessels into 

 which the ovarian or spermatic 

 veins open. 



It is obvious, therefore, that in 

 both Amiurus and Anguilla the 

 primitive direct continuity of the 

 caudal and posterior cardinal 

 veins has been interrupted by the 

 formation of a well - developed 

 renal portal system, and further, 

 that tlie residue of the caudal 

 venous blood finds its way to 

 the liver through the hepatic 

 portal vein ; hence it follows that, 

 as in so many of the lower air- 

 breathing Vertebrates, the whole 

 of the venous blood from the tail 

 is distributed either to the kidneys 

 or liver in the course of its return 

 journey to the heart. 

 Tig. 188.— Renal portal circulation in the The Tench (Tinca vulgaris) 

 ^A [Anguilla vidgaris). c.^, Caudal exhibits the interesting anomalv 



vein ; i.v, intestinal vein ; Lp.c, r.p.c, ^ . a j 



left and right posterior cardinal of poSSCSSing twO Caudal VeinS, 



veins; ^..,>, hepatic portal vein ; ij g, dorsal and a Ventral (Fig. 189). 



luduey ; r.jp.v, r.ji.v , renal portal , ^^uiiij. ^^ ■'&• j-^^j. 



veins ; sg.v, segmental veins ; x, arch- The dorsal vein is directly COn- 



like anastomoses between the renal f;„,-.^,-,r. x,,;*-!, j-T, • i,j- j. ■ 



portal and hepatic portal veins ; y, tmUOUS With the right posterior 



vein from the urinary bladder. (From cardinal, while the Ventral One 



divides into three branches, two 

 forming right and left renal portal veins and receiving numerous 

 segmental veins, and the third becoming one of the affluents of 

 the hepatic portal vein. In this Teleost it is clear that a 

 portion of the caudal blood passes directly to the heart through 

 the right posterior cardinal without traversing either the renal 

 portal or hepatic portal system. 



In the Cod (Gadus morrhua) the caudal vein divides into two 

 branches. The larger right vein retains its direct continuity 



