THE DEEP VEINS OF I HE LOWER EXTREMITY 751 



the two sides unite at an acute angle to form the inferior vena cava. The right 

 common iliac (v. iliaca communis dextra) is shorter than the left, nearly vertical in 

 its direction, and ascends behind and then to the outer side of its corresponding 

 artery. The left common iliac (v. iliaca communis sinistra), longer than the right, 

 and more oblique in its course, is at first situated on the inner side of the corre- 

 sponding artery, and then behind the right common iliac. Each common iliac 

 receives the iliolumbar, and sometimes the lateral sacral veins. The left receives, 

 in addition, the middle sacral vein. No valves are found in these veins. 



The middle sacral veins (Figs. 522 and 523) accompany the corresponding 

 artery along the front of the sacrum, and join to form a single vein (v. sacral is 

 media), which terminates in the left common iliac vein; occasionally in the angle 

 of junction of the two iliac veins. The middle sacral veins communicate with 

 the inferior hemorrhoidal. 



The iliolumbar veins (rr. iliolumbales) receive branches from the iliac fossa?, 

 spinal muscles, and vertebral canal. One vein on each side runs with the artery, 

 passes posterior to the Psoas muscle, and joins the common iliac vein. 



Peculiarities. The left common iliac vein, instead of joining with the right in its usual 

 position, occasionally ascends on the left side of the aorta as high as the kidney, where, after 

 receiving the left renal vein, it crosses over the aorta, and then joins with the right vein to form 

 a short inferior vena cava. In these cases the two common iliacs are connected by a small 

 communicating branch at the spot where they are usually united. 



The inferior vena cava (postcava, v. cava inferior) (Figs. 515 and 522) returns 

 to the heart the blood from all the parts below the Diaphragm. It is formed by 

 the junction of the two common iliac veins on the right side of the intervertebral 

 substance between the fourth and fifth lumbar vertebrae. It passes upward along 

 the front of the vertebral column on the right side of the aorta, and, having 

 reached the liver, is contained in a groove on its posterior surface. It then 

 perforates the Diaphragm between the mesal and right portions of the central 

 tendon; it subsequently inclines forward and inward for about an inch, and, 

 piercing the fibrous pericardium, passes behind the serous pericardium to open 

 into the lower and back part of the right auricle. In front of its auricular orifice 

 is a semilunar valve, the Eustachian valve (valvula v. cavae inferioris [Eustachii]); 

 this is rudimentary in the adult, but is of large size and exercises an important 

 function in the fetus. 



Relations. In front, from below upward, with the mesentery, right spermatic artery, trans- 

 verse portion of the duodenum, the pancreas, portal vein, and the posterior surface of the liver, 

 which, in most cases, partly and occasionally completely surrounds it; behind, with the verte- 

 bral column, the right crus of the Diaphragm, the right renal and lumbar arteries, the right 

 semilunar ganglion, and the inner part of the right suprarenal gland; on the right side, with 

 the right kidney and ureter; on the left side, with the aorta. The thoracic portion is short and 

 covered anterolaterally by the serous layer of the pericardium. 



Peculiarities. In Position. This vessel is sometimes placed on the left side of the aorta, 

 as high as the left renal veins, after receiving which it crosses over to its usual position on the 

 right side; or it may be placed altogether on the left side of the aorta, as far upward as its ter- 

 mination in the heart; in such cases the abdominal and thoracic viscera, together with the great 

 vessels, are all transposed. The vessel may be double, due to the bilateral persistence of the 

 cardinal veins. 



Point of Termination. Occasionally the inferior vena cava joins the vena azygos major, 

 which is then of large size. In such cases the superior vena cava receives the whole of the 

 blood from the body before transmitting it to the right auricle, except the blood from the 

 hepatic veins, which passes directly into the right auricle. 



Applied Anatomy. Thrombosis of the inferior vena cava is due to much the same causes 

 as that of the superior (see page 740). It usually causes edema of the legs and back, without 

 ascites; if the renal veins are involved, blood and albumin will often appear in the urine. An 

 extensive collateral venous circulation is soon established by enlargement either of the super- 

 ficial or of the deep veins, or of both. In the first case the epigastric, the circumflex iliac, the 



