The ureter descends
on the medial edge of psoas major, which separates it from the
transverse processes of L2–L5, and is crossed by the gonadal
vessels; it is at risk when these are ligated and divided in
gynaecological surgery. On the right, the ureter passes behind
the third part of the duodenum before it emerges immediately
deep to, and adherent to, the peritoneum of the posterior
abdominal wall. On the left it passes behind the apex of the
sigmoid mesocolon. It passes into the pelvis very constantly at
the bifurcation of the common iliac artery, even when this vessel
becomes tortuous and distorted in arteriosclerosis.