The common iliac arteries are two large arteries, about 4cm long in adults but more than a centimetre in diameter, that originate from the aortic bifurcation. The arteries run inferolaterally, along the medial border of the psoas muscles to the pelvic brim, where they bifurcate into the external iliac artery and internal iliac artery. The common iliac artery, and all of its branches, exist as paired structures (that is to say, there is one on the left side and one on the right). The distribution of the common iliac artery is basically the pelvis and lower limb on the corresponding side. Both common iliac arteries are accompanied along their course by common iliac veins. [WP,unvetted]. [ http://en.wikipedia.org/wiki/Common_iliac_artery ]