VENOUS SYSTEM. 



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correspond in their distribution to those of the 

 artery of the same name, and communicate 

 freely with the lower lumbar and sacral veins. 



(I}) The middle sacral vein. A single trunk 

 placed on the sacrum in the middle line, 

 which communicates inferiorly with the vesi- 

 cal and hnemorrhoidal plexuses, and on each 

 side with the adjacent lateral sacral veins. It 

 usually opens into the left common iliac vein, 

 but sometimes terminates more symmetrically, 

 by bifurcating and giving a branch to either 

 common iliac vein. 



(f) The lateral sacral veins. These ana- 

 stomose very freely with the middle sacral and 

 glutaeal veins, and with veins in the sacral 

 canal, before terminating in the common iliac 

 veins. 



Inferior vena cava. (Vena cava ascen- 

 dens.) 



This vein, the largest in the body, since 

 it returns to the heart all the blood which is 

 circulated below the diaphragm, is formed by 

 the junction of the common iliac veins, just 

 as the superior cava is constituted by that of 

 the venae innominatae. The abdominal vena 

 cava passes upwards in front of the lumbar 

 vertebrae, behind the liver and on the right side 

 of the aorta. At first the inferior vena cava 

 and the aorta are in close contact ; but as they 

 ascend, the vein inclines forwards and to the 

 right side, so that in the vicinity of the dia- 

 phragm these great blood-vessels become more 

 and more remotely related to each other, and 

 finally, the thoracic duct, the vena azvgos, the 

 right splanchnic and sympathetic nerves, the 

 right crus of the diaphragm and the Spigeliau 

 lobe of the liver intervene between them. The 

 anterior relations of the inferior vena cava are 

 the following : the peritoneum, the mesentery, 

 the inferior portion of the duodenum, the 

 pancreas, the commencement of the vena 

 portae, and the liver, which latter sometimes 

 forms a complete canal for the cava. Pos- 

 teriorly, the inferior cava corresponds to the 

 vertebrae, to the psoas muscle, and to the 

 right renal and right lumbar arteries : exter- 

 nally, it is related to the right kidney. 



The inferior vena cava is not uniform in its 

 dimension?, for it presents two remarkable 

 dilitations in its course, the first where it is 

 joined by the emulgent veins, and the second, 

 opposite to its junction with the venae cavae 

 hepaticae. 



Having passed behind, or through, the liver, 

 the vena cava is transmitted through the 

 *' foramen quadratum " of the diaphragm, and 

 at the same time penetrates the fibrous layer 

 of the pericardium, which is here intimately 

 connected with the cordiform tendon of the 

 diaphragm. Above the diaphragm the vena 

 cava bends abruptly to the left, and, after a 

 very short, and almost transverse course 

 within the pericardium, during which it is in- 

 vested on its anterior surface by the serous 

 membrane, terminates by entering the most 

 posterior and inferior portion of the right 

 auricle ; the axis of its opening is directed 

 upwards, backwards, and to the left side. 

 There are no valves in this vessel. 



Collateral branches. Besides the common 

 iliac veins, which are its formative roots, the 

 inferior vena cava receives the following, vie., 

 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, 



() 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, which 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 pampinifornm). 

 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 (lumbo-vertcbral 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 parieties of the abdomen, where they are 

 connected with the epigastric veins, and on 

 both sides pass behind the psoae 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 



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