Internal genital pathways

The internal genital ducts develop mainly from the mesonephric duct and paramesonephric duct. The former arises at S11 (urinary system) whilst the latter first appears at S16. The paramesonephric duct begins with invagination of the coelomic epithelium at the lateral aspect of the mesonephric ridge, close to its cranial end. It grows as a solid cellular cord caudally in the mesonephric ridge, and becomes canalized later. The paramesonephric duct grows medially at the caudal end of the mesonephros and crosses the mesonephric duct ventrally. At S22, it joins the paramesonephric duct from the other side. Together they grow further caudally. Both ducts reach the urogenital sinus during month 3. The caudal parts of the paramesonephric ducts run parallel to each other. They fuse together to form the uterovaginal canal (canalis uterovaginalis or primordium uterovaginale). Their closed ends cause an elevation in the region of the urogenital sinus: the Müllerian tubercle (sinual tubercle).