The vas deferens (plural: vasa deferentia), also called ductus deferens (Latin: "carrying-away vessel"; plural: ductus deferentes), is part of the male anatomy of many vertebrates; they transport sperm from the epididymis in anticipation of ejaculation. Structure There are two ducts, connecting the left and right epididymis to the ejaculatory ducts in order to move sperm. Each tube is about 30 centimeters long (in humans) and is muscular (surrounded by smooth muscle). Its epithelium is lined by stereocilia. They are part of the spermatic cords. The ductus deferens consists of three coats: (1) an external or areolar coat (2) a muscular coat consists of two layers of unstriped muscular fiber: an outer, longitudinal in direction, and an inner, circular; but in addition to these, at the commencement of the ductus, there is a third layer, consisting of longitudinal fibers, placed internal to the circular stratum, between it and the mucous membrane (3) an internal or mucous coat, which is pale, and arranged in longitudinal folds. The mucous coat is lined by columnar epithelium which is non-ciliated throughout the greater part of the tube; a variable portion of the testicular end of the tube is lined by two strata of columnar cells and the cells of the superficial layer are ciliated. Function in ejaculation During ejaculation, the smooth muscle in the walls of the vas deferens contracts reflexively, thus propelling the sperm forward. This is also known as peristalsis. The sperm is transferred from the vas deferens into the urethra, collecting secretions from the male accessory sex glands such as the seminal vesicles, prostate gland and the bulbourethral glands, which form the bulk of semen. Significance in contraception The procedure of deferentectomy, also known as a vasectomy, is a method of contraception in which the vasa deferentia are permanently cut, though in some cases it can be reversed. A modern variation, which is also known as a vasectomy even though it does not include cutting the vas, involves injecting an obstructive material into the ductus to block the flow of sperm. Investigational attempts for male contraception have focused on the vas with the use of the intra vas device and reversible inhibition of sperm under guidance. Blood supply The vas deferens is supplied by an accompanying artery (artery of vas deferens). This artery normally arises from the superior (sometimes inferior) vesical artery, a branch of the internal iliac artery.