From the latter organs the blood is collected by a series of renal veins, and by them conveyed to the posterior cardinals, and thence to the Cuvierian ducts. In the adult, therefore, there is a well-developed renal portal system, but it is worthy of note, nevertheless, that this system is developed comparatively late in embryonic life, and that at an earlier stage the caudal vein is directly continuous with the two posterior cardinals, precisely as is the case in the Cyclostomata throughout life. The posterior cardinal veins are situated in the dorsal wall of the coelom (Fig. 187), beneath the vertebral column. For the hinder portion of {317}their extent they are embedded in the kidneys (Fig. 186); and in this region the two veins are in close relation in the median line, and here and there freely communicate with each other. More anteriorly, they enlarge so much that they present the appearance of cavernous sinuses. In addition to the anterior segmental and oviducal veins, the posterior cardinals receive the spermatic or the ovarian vein from the male or female gonad. The precaudal section of the primitive subintestinal vein, now termed the internal intestinal vein (Figs. 186 and 187), traverses the spiral valve as it passes forwards to the liver, but from a physiological point of view is now merely one of the factors of the great hepatic portal vein, the principal tributaries of which are the veins from the stomach and intestine, including the rectal gland, and the pancreas and spleen. On entering the liver the hepatic portal vein divides into two principal branches for the right and left halves of the gland. From the liver the blood is conveyed by two hepatic veins to the sinus venosus. [Illustration: FIG. 186.—Venous system of _Mustelus antarcticus_. _a_, Auricle; _a.c_, anterior cardinal; _b.a_, conus arteriosus; _br.v_, brachial vein; _c.d_, Cuvierian duct or precaval vein; _c.v_, caudal vein; _cl.v_, cloacal vein; _f.v_, femoral vein; _h.s_, hyoidean sinus; _h.v_, hepatic vein; _i.i.v_, internal intestinal vein; _i.j_, inferior jugular; _k_, kidney; _l_, liver; _l.v_, lateral vein; _md.v_, mandibular vein; _n.h.v_, nutrient hyoidean veins; _o.s_, orbital sinus; _p.c_, posterior cardinal; _p.v_, hepatic portal vein; _rp.v_, renal portal vein; _sc.v_, subscapular vein; _sp.v_, spermatic vein; _s.v_, sinus venosus; _v_, ventricle; _v.a_, ventral aorta. (After T. J. Parker.)] The lateral veins (Fig. 186) are situated in the lateral walls {318}of the abdomen, immediately external to the peritoneum (Fig. 187). Each vein begins near the pelvic fin, where it is connected with its fellow across the dorsal face of the ischio-pubic cartilage, and thence runs forward towards the pectoral fin. At its origin the lateral vein receives a femoral vein from the pelvic fin and a cloacal vein, and also, near its anterior end, a brachial vein from the pectoral fin, finally joining the Cuvierian duct of its side.[361]