Up to the 7th week the internal genital organs in both sexes on both sides consist of two canal systems:
- The mesonephric duct and the mesonephric tubules, which first form on the dorsal side of the nephrogenic cord at the level of the 9th somite in the form of solid, cellular mesenchymal cords (stage 11). They detach themselves from the nephrogenic cord and are located below the coelomic epithelium that is thickened at this place. The detailed description of the development of the mesonephric duct can be found in the urinary system module.
- The paramesonephric duct (Müller) is formed from a finger-shaped invagination of the coelomic epithelium on the upper pole of the mesonephros. It forms here a funnel that opens into the coelomic cavity (future ampulla of the fallopian tube).
The paramesonephric duct invades on both sides - laterally to the mesonephric duct - into the mesonephros and grows in the caudal direction. At the lower end of the mesonephros the paramesonephric duct crosses over the mesonephric duct in order to grow further medially. There, the paramesonephric ducts meet on both sides and fuse to form a canal ((the future uterus).They then push on the urogenital sinus, forming a small protrusion, the paramesonephric tubercle.