904 HUMAN ANATOMY. 



uterus. Leaving the broad ligament with the ovarian artery, they ascend along 

 that vessel, the number of trunks becoming reduced to two and eventually to one, 

 and they open above in the same manner as the spermatic veins, the right one 

 into the inferior vena cava and the left one into the left renal vein. They possess 

 1:0 valves. 



Their variations are essentially similar to those presented by the spermatic veins. 



Practical Considerations. — The Tributaries of the Inferior Cava. — In a 

 case of occlusion of the inferior cava by thrombus extending from the renal vein to 

 the right auricle, the phrenic and reyial veins opened into the Iinnbar and azygos 

 veins, the blood of the abdomen thus gaining the superior cava (Allen). 



The intralobular branches of the hepatic veins may be the source of profuse 

 hemorrhage in cases of wound or rupture of the liver, because {a') they are thin- 

 walled ; i^b') they are not encircled by cellular tissue, but are closely attached to the 

 liver substance and thus cannot collapse or retract, a condition which also predisposes 

 to the entrance of air into the divided veins ; {c~) they are valveless, and the main 

 trunks open direct into the vena cava, any obstruction of which would therefore result 

 in the escape of great quantities of blood ; (af ) the flow in the main trunks — from the 

 vein to the cava — is influenced by the movements of the diaphragm, the descent of 

 this muscle tending to constrict the opening through which the veins pass, and thus 

 to obstruct the current and favor bleeding. Hemorrhage from the liver after a wound 

 or during an operation is very difficult to arrest by ligature on account of the thinness 

 of the walls of the intralobular veins and the friability of the liver tissue itself. It is 

 usually controlled by gauze-pressure or by the gahano-cautery. The branches of the 

 portal vein may also bleed freely, but are surrounded by a quantity of lax cellular 

 tissue, as they run in the ' ' portal canals' ' with the branches of the biliary ducts and 

 of the hepatic artery, and can thus retract or collapse when torn or divided. More- 

 over, the blood-pressure within the portal vein is low, favoring the spontaneous arrest 

 of hemorrhage. In obstruction of the common duct, preventing the escape of bile 

 into the intestine, the radicles of the hepatic veins take up the bile-stained exudate 

 that results from the increased intra-hepatic tension. Its entrance into the general 

 circulation through the vena cava gives rise to jaundice. 



The relative shortness of the right renal Aein occasionally adds to the difficulties 

 of a right-sided nephrectomy, the pedicle — the vein, artery, ureter, etc. — being 

 shorter and less easily controlled by ligature. As the veins are subject to variation 

 as well as the arteries — though less frequently — supernumerary or misplaced vessels 

 should be carefully looked for. They may be found emerging from the kidney at 

 either pole, or from the hilum behind the pelvis. Fatal results have followed the 

 failure, during a nephrectomy, to find and secure such aberrant vessels. At times 

 the left renal vein passes behind the aorta, to which occurrence may be attributed 

 the greater frequency of hyperaemia of the left kidney (Allen). The renal veins 

 may be obstructed by pressure from retroperitoneal growths, or — in the supine 

 position — from movable abdominal tumors or the gravid uterus, or from traction 

 '^aused by displacements of the kidney itself, or as a result of congestion in the 

 cardio-pulmonary system, as in pneumonia or valvular heart disease. By whatever 

 cause produced, the congestion, if sufficiently long-continued, may give rise to a form 

 of chronic interstitial nephritis. The communication {vide supra) between the renal 

 veins and the first lumbar vein and — on the left side — the hemiazygos vein, accounts 

 for the undoubted good effect often produced in renal congestions by counter- 

 irritation, blisters, cupping, or leeching in the loin. 



The spermatic veins are of chief practical interest in their relation to varicocele. 

 The anatomical reasons for the frequency of this condition, and for its occurrence by 

 preference on the left side, are given on page 1961. 



The veins of the pampiniform plexus proper are usually distinct from those 

 which accompany the vas deferens and its artery. In excision of the former set for 

 varicocele, the vas deferens is always pushed to the rear and held out of harm's way. 

 It carries with it its artery and veins, and the anastomotic communications of the 

 former with the spermatic artery — almost always cut or tied with its venous plexus — 

 and with the scrotal arteries suffice to maintain the nutrition of the testis, while the 



