THE INFERIOR CAVAL SYSTEM. 901 



Assure. Its relation to the right psoas major muscle has resulted, in cases of psoas 

 abscess, in ulceration and opening of the vein, with fatal hemorrhage. Its relation 

 to the inner border of the right kidney has resulted in its compression by a 

 movable kidney, or by a cancerous growth of the kidney, causing caval thrombosis, 

 a condition which has also been noted in connection with chronic nephritis and 

 with infarction of the renal parenchyma. Its relation to the liver results, in 

 some cases of hepatic enlargement, in compression of the vena cava with oedema 

 of the lower limbs, and other symptoms of obstruction. Its close proximity to 

 the lower end of the bile-duct necessitates caution in cutting operations for the 

 removal of impacted stones from the duct (choledochotomy) (page 1732). Enlarge- 

 ment or growth involving the head of the pancreas may compress the cava 

 sufificiently to cause obstructive symptoms, and the nearness of the vein constitutes 

 one of the very serious obstacles to removal of pancreatic tumors. In ureterotomy 

 or other operation on the right ureter, the close relationship of the vena cava at 

 the point of crossing should be remembered. Thrombosis of the cava, from 

 whatever cause, though it may extend the entire length of the vessel, is apt to 

 be limited to a portion of the vessel, as that between the renal veins and the 

 auricle, or that extending from the iliac veins to the renal veins. The collateral 

 circulation after occlusion may be carried on through the saphenous, superficial 

 abdominal, spermatic, pudic, and deep epigastric veins, and the obturator, inferior 

 mesenteric, external mammary, and azygos veins. 



Tributaries. — In addition to the common iliac veins by whose union it is 

 formed, the vena cava inferior receives a number of tributaries from the abdominal 

 walls and organs. These may be arranged into two groups according as they drain 

 i\\Q parietes of the abdomen (radices parietales) or its viscera (radices viscerales). Of 

 the former there are : (i) the ijiferior phrenic and (2) the lumbar veins, and of the 

 latter (3) the Jiepatic, (4) the roial, (5) the suprarenal, and (6) the spermatic or 

 ovarian veins. 



1. The Inferior Phrenic Vein. — The inferior phrenic (v. phrenica inferior) 

 is a paired vein which corresponds to the similarly named artery. It is formed by 

 the union of a number of tributaries which ramify upon the under surface of the 

 diaphragm, and opens into the vena cava just before it passes through the diaphragm. 

 It receives tributaries from the upper portion of the suprarenal capsule, and the left 

 vein, by the enlargement of an anastomosis of its suprarenal tributaries with the 

 suprarenal vein, may open through the latter into the left renal vein. The right 

 vein occasionally opens into the right hepatic vein. 



2. The Lumbar Veins. — The lumbar veins (vv. lumbales) are usually four in 

 number on each side, and accompany the corresponding arteries, lying above them. 

 They resemble closely in their relations and tributaries the intercostal veins, of which 

 they are serial homologues. Each vein arises in the muscles of the abdominal wall 

 and passes backward and inward towards the vertebral column, passing beneath the 

 psoas muscle. Shortly before reaching the vena cava it receives a ramus dorsalis. 

 This has its origin in the dorsal integument and muscles, communicating with the 

 posterior external spinal plexus, and receives a ramus spinalis which communicates 

 with one of the lumbar intervertebral veins and so with the internal spinal 

 plexuses. The veins then continue their course towards the vena cava, those of the 

 left side passing beneath the abdominal aorta, and they open into the posterior 

 surface of the vena cava. 



As it passes upon the lateral surface of its corresponding lumbar vertebra, each 

 of the three lower veins is connected with the one above by an ascending stem, which 

 also places the lowest vein in communication with the ilio-lumbar or the common iliac 

 vein, while from the uppermost vein it is continued on upward to -join with the azygos 

 or hemiazygos as the case may be. This ascending stem is the ascending lumbal 

 vein (v. lumbalis ascendens), and is of especial interest as forming an important 

 collateral channel between the inferior and superior venae cavae. 



Each lumbar vein possesses one or two valves in its course, and sometimes 

 also valves at its entrance into the vena cava. The concavities of these valves are 

 directed towards the vena cava, but the valves are nearly always insufificient and 



