[Embryological study of the mechanism of antenatal lower urinary tract obstruction].

Closure of the embryonic bladder based on the results of the study of 25 human embryos (Crown-Rump length: 5mm-60mm) and 8 Born's reconstructions, is presented. It is a complex but well regulated stage of organogenesis. Division of the cloaca depends on caudal regression, development of the genital tubercle and growth of the urorectal fold which joins the cloacal membrane.