cloaca(redirected from cloacae)
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the broadened extremity of the hindgut of some vertebrate animals. The wall of the cloaca is covered with a many-layered epithelium. The ureter, the genital ducts (sperm ducts or oviducts), and the urinary bladder open into the cloaca. It is found in certain cyclostomes (hagfish) and fishes (sharks, skates, dipnoans and pipefish) and in all amphibians, reptiles, and birds. The cloaca is found in mammals of the subclass Prototheria. In other mammals a cloaca is found only in the early embryonic stage of development; it subsequently divides into the urogenital sinus and the terminal part of the rectum, which have separate urogenital and anal openings. In amphibians the urinary bladder is formed from an evagination of the abdominal wall of the cloaca. Allantoides appear in the embryo of amniotes.