Metanephros or definitive kidney

The metanephros develops through the interactions between three components: 1) the epithelial ureteric bud, 2) the mesenchymal metanephrogenic blastema, 3) the ingrowing vessels.
At S14, the ureteric bud sprouts from the caudal part of the mesonephric duct (level of the first sacral segment) dorsally as an epithelial diverticulum. It enlarges at its end to form an ampulla, and becomes surrounded by a condensed metanephrogenic blastema. The part of the ureteric bud linked to the ampulla extends and becomes the ureter. The part of the mesonephric duct situated caudally to the root of the ureteric bud is now known as the common excretory duct.