ABSTRACT
A bud from the lower end of the mesonephric (wolffian) duct grows backwards behind the peritoneum to the sacral region. The stalk of the bud forms the ureter and its dilated upper extremity, the renal pelvis. From 6 weeks to 8 months of gestation, the primitive pelvis bifurcates repeatedly to form first the calyces and, after several subsequent divisions, the collecting ducts.
