The membrane that covers the embryonic cloaca, formed by the union of proctodeal (anal pit) ectoderm and cloacal endoderm, with no intervening mesoderm; the urorectal septum joins the cloacal membrane and divides it into an anal membrane and a urogenital membrane; the point where the urorectal septum intersects the cloacal membrane is the future site of the perineal body; proliferation of mesoderm and ectoderm around the cloacal membrane produces primordial tissues of the external genitalia in both sexes: the genital tubercle, genital folds, and genital swellings.

http://upload.wikimedia.org/wikipedia/commons/d/d2/Gray991.png

A membrane that separates the proctodeum and the hindgut in the early embryo. [Evolution, Fourth_Edition_(2006)_McGraw-Hill, Function, Vertebrates:_Comparative_Anatomy, p.497, see_Kardong_KV][VHOG]

embryonic cloacal membrane

uberon

membrana cloacalis

In mammals, the cloaca exists as an embryonic structure that undergoes septation to become distinct urethral, anal, and genital orifices.[well established][VHOG]

UBERON:0006217

http://purl.obolibrary.org/obo/uberon.owl, http://purl.obolibrary.org/obo/cl.owl

• embryonic cloacal fold