3i6 THE VASCULAR SYSTEM 



duodenum, the epiploic foramen (of Winslow) and the liver. 

 It pierces the diaphragm opposite the fibre-cartilage between 

 the eighth and ninth thoracic vertebrae and at once enters the 

 lowest part of the right atrium (auricle) of the heart. 



As it ascends through the abdomen, the inferior vena cava 

 receives numerous tributaries. Below the head of the 

 pancreas, it is joined by the lower lumbar and the right 

 spermatic (or ovarian) veins. As it lies behind the head of 

 the pancreas, it receives both renal veins and, just before it 

 pierces the diaphragm, it receives the right and left hepatic 

 veins. 



The signs produced by obstruction of the inferior vena 

 cava v^ry according to the site of the obstruction. When it 

 is compressed near its origin, there may be little or no ascites 

 and the venous stasis is most evident in the lower limbs. 

 Swelling of the feet and ankles and dilatation of the superficial 

 veins of the leg are always present. When the obstruction is 

 very great, an effort is made to bring about compensation by 

 the establishment of a new channel of return to the heart. The 

 superficial veins of the lower part of the anterior abdominal wall 

 pour their blood into the femoral vein, and so it ultimately 

 reaches the inferior vena cava. On the other hand, the veins 

 from the upper part of the anterior abdominal wall pour their 

 blood into the intercostal and lateral thoracic veins, which are 

 ultimately tributaries of the superior vena cava. These two 

 groups communicate freely with one another, and, as they are 

 devoid of valves and as the loose superficial fascia in which 

 they lie permits of, a large degree of dilatation, the anastomosing 

 channels become greatly enlarged when the inferior vena cava 

 is obstructed. In this condition, therefore, it is usually found 

 that the superficial veins of the abdominal and thoracic walls 

 are enormously dilated. The condition is somewhat similar 

 to the " Caput Medusae " appearance found in portal obstruc- 

 tion (p. 276), but presents this essential difference that, 

 whereas in portal obstruction the blood-flow radiates in both 

 directions from the umbilicus, in obstruction of the inferior 



