Cloaca (embryology)
（重定向自Cloacal duct）
The cloaca is a structure in the development of the urinary and reproductive organs.
The hind-gut is at first prolonged backward into the body-stalk as the tube of the allantois; but, with the growth and flexure of the tail-end of the embryo, the body-stalk, with its contained allantoic tube, is carried forward to the ventral aspect of the body, and consequently a bend is formed at the junction of the hind-gut and allantois.