part of part of cloaca sphincter muscle cloacal sphincter UBERON:0013501 sphincter cloacae NCIT:C34129 the muscles of the cloacal sphincter specialise into the perineal muscles in mammals (Gegenbaur, 1883; Popowsky, 1899; Nishi, 1938). A sphincter muscle that is part of a cloaca. cloacal muscle