VASCULAR SYSTEM 



321 



sg.v! 



with the corresponding posterior cardinal ; the left, on the con- 

 trary, has ceased to be continuous with the greatly reduced left 

 posterior cardinal and forms a renal portal vein, the distribution 

 of which is, however, restricted to the hinder portion of the left 

 kidney (Fig. 190). As in Amiurus, a branch of the caudal vein 

 forms one of the tributaries of 

 the hepatic portal vein. In the 

 Cod it would therefore seem 

 that only a relatively small 

 proportion of the caudal blood 

 flows through the imperfectly 

 developed renal portal system, 

 the bulk of it traversing the 

 right posterior cardinal and 

 passing directly to the heart, 

 leaving, nevertheless, a modi- 

 cum for transmission to the 

 liver. Finally, it may be 

 mentioned that in some Teleosts 

 the caudal vein retains its em- 

 bryonic continuity with one, 

 usually the right, posterior 

 cardinal, without giving off a 

 renal portal affluent, as in the 

 Perch (Perca fluviatilis) ; or, 

 after division, with both pos- 

 terior cardinals, as in the 

 Lump - sucker (Cydopterus 

 lumpus). In such instances as 

 these no portion of the caudal 

 blood traverses the kidneys, 



FIG. 189. Renal portal system in the Tench 

 (Tinea vulgaris). d.c.v, v.c.v, Dorsal and 

 ventral caudal veins ; k, kidney ; l.p.c, 

 r.p.c, left and right posterior cardinal 

 veins ; p.v, hepatic portal vein ; r.p.v, 

 renal portal vein ; sg.v, sg.v', segmental 

 veins. (From Jourdain.) 



and if a renal portal system 

 exists at all, the only true 

 renal portal veins are the ad- 

 jacent segmental veins, which transmit venous blood directly to 

 the kidneys, instead of first uniting with renal portal branches of 

 the caudal vein as in the Tench and the Eel. 



Whatever may be the condition of the renal portal system, all 

 the renal blood is eventually collected by renal veins and conveyed 

 to the posterior cardinals, which are often connected by one or 



VOL. VII Y 



