The common iliac arteries, [a. iliacae communes], commencing at the bifurcation of the aorta, pass downwards and outwards, diverging from each other, and divide opposite the intervertebral substance between the last lumbar vertebra and the sacrum, into two branches, named the internal and external iliac arteries — the former being distributed to the walls and viscera of the pelvis, whilst the latter is prolonged into the lower limb, after having sent two important branches to the walls of the abdomen.

The common iliac arteries usually measure about two inches in length. They are both covered by the peritoneum and the intestines, and rest on the bodies of the vertebrae, approaching respectively the psoas muscles at their ends ; they are crossed by the ureters at their point of division, and likewise by the branches of the sympathetic nerve, which are directed towards the hypogastric plexus.

The common iliac arteries of opposite sides differ in some degree in their connections with other parts, but more especially with the neighboring veins. Thus, the artery of the right side is placed at a distance from the front of the last lumbar vertebra, the two common iliac veins being interposed. The artery of the left side is crossed by the branches of the inferior mesenteric artery.

Veins

The left iliac vein, supported on the last lumbar vertebra, lies to the inner side of, and below the left artery. On the right side there are three veins in connection with the artery; the right iliac vein lying behind the lower part of the vessel, the iliac vein of the left side crossing behind it, and the vena cava (resulting from the union of the two others) being on the right side of the artery at its upper end.

From Quain's anatomy.