Embryology

Niharika Nixit MD Ashley Davidoff MD

In females, in the absence of MIS (Mullerian inhibiting substance) and androgens, the nephric (wolffian) ducts degenerate, and the paramesonephric (müllerian) ducts give rise to the fallopian tubes, uterus, and upper two thirds of the vagina. The remnants of nephric ducts are found in the mesentery of the ovary as the epoöphoron and paroöphoron and near the vaginal introitus and anterolateral vaginal wall as Gartner’s duct cysts. The distal tips of the paramesonephric ducts adhere to each other just before they make contact with the posterior wall of the urogenital sinus. The wall of the urogenital sinus at this point forms a small thickening called the sinusal tubercle. As soon as the fused tips of the paramesonephric ducts connect with the sinusal tubercle, the paramesonephric ducts begin to fuse in a caudal to cranial direction, forming a tube with a single lumen. This tube, called the uterovaginal canal, becomes the superior portion of the vagina and the uterus. The unfused, superior portions of the paramesonephric ducts become the fallopian tubes (oviducts), and the funnel-shaped superior openings of the paramesonephric ducts become the infundibula.