474 LOWER VENA CAVA. 



abdominal ring there are numerous convoluted branches forming the spermatic 

 plexus (plexus pampiniformis). These branches gradually unite, and form a 

 single vessel, which opens on the right side into the lower vena cava, and on 

 the left into the renal vein. The spermatic veins sometimes bifurcate before 

 their termination, each division opening separately ; in this case, the veins 

 of the right side may be found communicating with the vena cava and the 

 renal vein. 



In the female the ovarian veins have the same general course as the 

 ovarian arteries ; they form a plexus near the ovary (ovarian or pampiniform 

 plexus) in the broad ligament, and communicate with the uterine plexus. 



Valves exist in the spermatic veins in man (Monro) ; and, in exceptional 

 cases, they have been also seen in the ovarian veins (Theile). 



d. The renal or emulgent veins are short, but of very considerable size. 

 That of the left side is longer than that of the right, and passes in front of 

 the aorta. They join the vena cava at nearly a right angle. The renal veins 

 usually receive branches from the suprarenal capsules ; the left has also 

 opening into it the spermatic vein of the same side. 



e. The capsular or suprarenal veins, though actually small, are, relatively 

 to the organs from which they arise, of considerable size. On the right 

 side the vein ends in the vena cava, and on the left in the renal or the 

 phrenic vein. 



/. The phrenic veins follow exactly the course of the arteries supplied to 

 the diaphragm by the abdominal aorta. 



g. The hepatic veins return from the liver the blood sent to that organ 

 by the portal vein and hepatic artery. They converge to the groove in 

 which the inferior vena cava lies, and pass at once obliquely into that vein. 

 There are usually three sets of hepatic veins proceeding to this common 

 point : those from the right and left lobes are oblique in their direction, 

 those from the middle of the liver and the lobule of Spigelius have an 

 intermediate position and course. The hepatic veins have no valves : but, 

 owing to their oblique entrance into the vena cava, a semiluuar fold is seen 

 at the lower border of the orifice of each vein. 



PECULIARITIES. The lower vena cava presents some occasional deviations from its 

 ordinary condition, which may be briefly noticed. 



In the lower part of its course, it is sometimes placed to the left side of 

 the aorta, and, after receiving the left renal vein, resumes its ordinary position by 

 crossing over the great* artery. Less frequently, the vena cava is placed altogether 

 on the left side, and is continued upwards to the heart, without any change in its 

 direction ; this occurs in cases of transposition of the thoracic and abdominal viscera 

 and of the great vessels. 



In a more numerous class of cases, the left common iliac vein, instead of joining 

 the right in its usual position, is connected with it only by a small branch, and then 

 ascends on the left side of the aorta. After receiving the left renal vein, it crosses 

 over the aorta, and terminates by uniting with the common iliac vein of the right 

 side. In these cases, the vena cava inferior can be said to exist only at the 

 upper part of the abdomen, and below this point there is a vein on each side of the 

 aorta. 



Lastly, the lower vena cava, instead of ending in the right auricle of the heart, 

 has been seen to join the right azygos vein, which is then very large ; eo that the 

 blood from the lower, as well as from the upper part of the body, is returned to the 

 heart through the upper vena cava. In this case, the hepatic veins do not join the 

 lower cava, but pass directly into the right auricle, at the usual place of termination 

 of the great vein. 



The left renal vein has been seen to cross behind the aorta. 



In a remarkable case, observed by Rothe, one of the hepatic veins ended, not in 



