320 FISHES CHAP. 
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 the 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. 
The Tench (Tinea vulgaris) 
exhibits the interesting anomaly 
of possessing two caudal veins, 
Fic. 188.—Renal portal circulation in the 
Eel (Anguilla vulgaris). ¢.v, Caudal 
vein ; 2.v, intestinal vein ; l.p.c, 7.p.c, 
left and right posterior cardinal 
veins ; p.v, hepatic portal vein; R, 
kidney ; 7.p.v, 7.p.v', renal portal 
veins ; sg.v, segmental veins ; x, arch- 
like anastomoses between the renal 
portal and hepatic portal veins; y, 
vein from the urinary bladder. (From 
Jourdain. ) 
a dorsal and a ventral (Fig. 189). 
The dorsal vein is directly con- 
tinuous with the right posterior 
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 
