This section is from the book "Anatomy Of The Arteries Of The Human Body", by John Hatch Power. Also available from Amazon: Anatomy of the Arteries of the Human Body, with the Descriptive Anatomy of the Heart.
The Left Common Iliac Artery descends with less obliquity than the right, and is usually shorter, in consequence of the aorta bifurcating on the left side of the spine. In many cases, however, it will be found longer, that is, the artery of the right side will bifurcate into its two terminating branches before it reaches the right sacro-iliac synchondrosis; whilst the left continues its course until it reaches this point at the left side: this fact, we believe, was first pointed out by Mr. Adams, of this city. Its posterior surface rests on the outer portion of the anterior common ligament, the fifth lumbar vertebra, and on the outer edge of its corresponding vein: the sympathetic, obturator and lumbo-sacral nerves also descend behind it as on the other side. Its anterior surface is covered by the peritoneum, and crossed obliquely by the ureter at its bifurcation; it is covered also by the sigmoid flexure of the colon and the termination of the inferior mesenteric artery. In the female, the vessels, analogous to the spermatic, are also related to it. It may be observed that the vein on this side is in no part of its course external to the artery, as on the opposite side. The psoae muscles are situated on the outside of the common iliacs, and between the two we see the middle sacral artery and part of the common iliac vein of the left side.
The common iliac arteries give off no branches before their bifurcation, except very minute ones to the ureters, peritoneum, iliac veins, and adjacent lymphatic glands. The common iliacs vary in their length, and bifurcate usually near the sacro-iliac symphysis into the external and internal iliac arteries.