Collateral branches. — Besides the common iliac veins, which are its formative roots, the inferior vena cava receives the following, viz., the renal, spermatic, (ovarian in the female), supra renal, lumbar, inferior phrenic, and hepatic veins.
(a) The renal veins are of great size, and pass transversely to join the cava ; the left is the longest ; it passes in front of the aorta to arrive at its destination, and is joined by the left spermatic, vein.
Both renal veins arise in the cortical sub stance of the kidneys by small radicles, which unite into larger vessels : these pass between the " pyramids," and so gain the hilus, where they lie in front of their accompanying arteries.
(b) The suprarenal, or capsular veins, are more numerous than the arteries of the same name ; there are usually three veins on each side, and but one artery. The veins are the superior, which joins the inferior phrenic, a middle, unites directly with the vera cava, and an inferior, which opens into the renal vein of its own side.
(c) The spermatic veins originate in the testis, and pass through the mediastinum testis. On entering the cord they receive veins from the epididymis, and assume a loose plexiform arrangement (plexus pampiniformis). The spermatic veins, now four or five in num ber, pass along the cord, and traverse the in guinal channel with the vas deferens and spermatic arteries. At the internal abdomi nal ring the spermatic veins leave the vas deferens and accompany their corresponding arteries, lying behind the peritoneum and in front of the psoas muscle. Continuing to
ascend, these veins cross the ureters external to the common iliac arteries, approximate to one another, and finally terminate, that of the right side in the vena cava, and that of the left side in the left renal vein.
In the abdomen there is either one sper matic vein, on each side, or two veins which freely communicate by short transverse branches, and unite in one common trunk before terminating.
In the female these vessels are represented by the Ovarian veins, which form a plexus between the layers of the broad ligament, and ter minate in the same manner as the spermatic veins in the male.
(d) Lumbar veins (lunibo-vertebral veins). — There are four or five pairs of lumbar veins which are in every respect analogous to the lumbar arteries from the aorta: they arise by muscular branches in the lumbar region, and in the parietics of the abdomen, where they are connected with the epigastric veins, and on both sides pass behind the psom muscles to open into the cava close to one another : the veins of the left side cross the spine be hind the aorta. The lumbar veins commu nicate very freely with the venous system of the spinal canal, with the ilio lumbar veins below, and with the commencement of the azygos veins superiorly.
(e) The inferior phrenic veins are derived from the diaphragm, and correspond accu rately to the phrenic arteries from the aorta.
The hepatic veins may be considered as forming an adjunct to the portal venous system, in connection with which they will be briefly noticed.