Fig. 189.—Renal portal system in the Tench (Tinca 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.)
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 by several transverse anastomoses (Fig. 190). In the region of the heart each posterior cardinal joins the corresponding anterior cardinal to form a short but wide Cuvierian duct, which finally opens into the sinus venosus.
A subintestinal vein is present in the embryo (e.g. Lepidosteus, Acipenser, and some Teleosts),[[363]] but in the adult Teleostome its precaudal section is usually absorbed, or at all events ceases to be recognisable except, perhaps, as one of the minor tributaries of the hepatic portal vein.[[364]]
The hepatic portal vein is formed as in Elasmobranchs, but in different Teleostomi it may also receive the veins from the pyloric caeca, from a portion of the air-bladder, the gonads, and, as previously mentioned, a tributary from the caudal vein. There are usually two hepatic veins opening into the sinus venosus, and generally of equal size (Fig. 190).
Fig. 190.—Venous system of a Teleost (diagrammatic). A, Auricle; ab.v, vein from the air-bladder; a.c, anterior cardinal; c.d, Cuvierian duct; c.p.c, transverse anastomoses between the two posterior cardinals; c.v, caudal vein; h.v, hepatic vein; i.j, inferior jugular; k, kidney; l, liver; p.c, left posterior cardinal; p.v, hepatic portal vein; r.p.c, right posterior cardinal; r.p.v, renal portal vein; sc.v, subclavian vein; sg.v, segmental vein; sp.v, spermatic vein; s.v, sinus venosus.
Most of the veins from the air-bladder join the hepatic portal vein, as already mentioned (Fig. 190), but more or fewer of them, especially those from the dorsal wall of the organ, open into the posterior cardinals. They may, as in Polypterus, even join the hepatic veins.[[365]]
The veins from the gonads are very variable in their destination, sometimes joining the posterior cardinals, as in the Salmon (Salmo salar); or the hepatic portal vein, as in Amiurus; or, as in the Perch (Perca fluviatilis), forming by their union a single trunk, which communicates directly with the left Cuvierian duct.
Representatives of the great lateral veins of Elasmobranchs appear to be absent in the Teleostomi, the veins from the pectoral and pelvic limbs joining the Cuvierian duct and the posterior cardinal veins respectively.