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). [Illustration: 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 {323}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. The two large anterior cardinal veins, which collect the blood from the head and brain, occupy their usual position directly above the branchial apparatus, and are sometimes connected by transverse anastomoses as they pass backwards to join the Cuvierian ducts. The inferior jugular vein is either single (e.g. _Gadus_); or paired, as in _Perca_ (Fig. 190). In the Dipnoi the venous system is distinguished by an interesting combination of characters, some of which are either primitive or peculiar to the group, while others exhibit a distinct transition to the embryonic or the adult condition of the lower air-breathing Vertebrates.