A duct on each side of the developing embryo or fetus that leads from the embryo's mesonephros, or temporary kidney. In male fetuses the duct persists as the Wolffian duct to form the rete testis, the epididymis, the vas deferens and the seminal vesicle. In female fetuses it usually disappears completely (in favor of the paramesonephric duct, better known as the Mullerian duct), though portions of mesonephric duct can remain as harmless cysts, called Gartner's duct cysts.

(pronounced 'mool-air-ian') Syn. paramesonephric duct. The internal female sex duct, which forms on each side of a female embryo to connect the peritoneal cavity with the outside of the embryo, starting at a point close to the ovary and forming first a fallopian tube then meeting its fellow from the other side to form the uterus, and then extending downwards to form the upper part of the vagina before finally connecting with a little dimple between the urethra (in front) and the anus (behind) to reach the exterior at the vulva. Passage of eggs from the ovaries (which ovulate into the peritoneal cavity of all vertebrate species) to the outside world through this duct is how animals, including humans, reproduce. In males the ducts do not develop because the Sertoli cells of the testes produce anti-Mullerian hormone.

The mesonephric duct.