Vv. iliacae communes, common iliac veins, right and left, merging with each other at the level of the lower edge of the IV lumbar vertebra, form the inferior vena cava. The right common iliac vein is located behind the artery of the same name, the left just below lies behind the artery of the same name, then lies medially from it and passes behind the right common iliac artery to merge with the right common iliac vein to the right of the aorta. Each common iliac vein at the level of the sacroiliac joint in turn is composed of two veins: the internal iliac (v. Iliaca interna) and the external iliac (v. Iliaca externa).