When the vas deferens leaves the internal abdominal ring it winds around the outer side of the deep epigastric artery and dips down over the brim of the pelvis 4 or 5 cm. (11/2 to 2 in.) posterior to the pubic spine. It then runs downward and backward on the side of the pelvis, under the peritoneum, crossing superficially the obliterated hypogastric artery, the obturator vessels and nerve, the vesical arteries, from the inferior of which it receives the artery of the vas, and finally the ureter. In its pelvic course the vas deferens is not often the subject of surgical interference except in cases of undescended testis. In these cases it is often loosened from the firm but thin fibrous bands which retain it in place, after which it is readily drawn forward to allow the testicle to descend.