The ductus deferens, or the vas deferens, is a male anatomical part; there are two of these ducts and their purpose is to carry ejaculatory sperm out of the epididymis. To do this, the left and right ductus deferens connect each side of the epididymis to the body's ejaculatory ducts. Each ductus deferens is supplied by the artery of vas deferens, which branches out of the superior vesicle artery. Each ductus deferens is a tube that is approximately 30 centimeters in length and protected by smooth muscle mass. This muscle mass contracts reflexively during ejaculation in a process called peristalsis. This is the process that allows sperm to flow through the ductus deferens and reach the urethra. On its way, the sperm collects secretions from the prostate gland, bulbourethral glands, and seminal vesicles, all male accessory sex glands. A permanent incision is made in each ductus deferens during a vasectomy, a male contraception method. A modern method of male contraception involves the injection of material into the ductus deferens to obstruct sperm flow. Sperm may remain active for up to 83 days no matter which procedure is used.