The ductus deferens is an extension of the same muscular duct that makes up the body and tail of the epididymis. It travels from the epididymis out of the scrotum as part of the spermatic cord, through the inguinal region or groin region to the urinary bladder. It then travels down the posterior surface of the bladder where it terminates as a wider distal region called the ampulla. The ampulla merges with a seminal vesicle to form the ejaculatory duct.
Figure 1: A labeled illustration of the ductus deferens. On the left is a midsagittal view of the entire system, and on the right a sagittal view of the testis.
The ductus deferens only functions during ejaculation. Ejaculation is an autonomic reflex that propels sperm from the epididymis to the outside of the body. During ejaculation, sperm are propelled by peristalsis of smooth muscle in the ductus deferens from the tail of the epididymis to the ejaculatory duct.