The Cloaca
The cloaca, common to the digestive and urogenital systems, opens to the exterior at the vent (Fig. 37.22/5). The colorectum, ureters, and deferent ducts (or the left oviduct) enter it at various levels.
The cloaca is divided sequentially into coprodeum, urodeum, and proctodeum by two more or less complete annular folds. The bursa of Fabricius is located in the dorsal wall of the proctodeum (Figs. 37.22/9 and 37.23).The coprodeum is the ampulliform continuation of the colorectum in which feces are stored (Fig. 37.22/2). In some desert species (e.g., budgerigar) it is lined with villi and is a site of water absorption. It is bounded caudally by the coprourodeal fold (Fig. 37.22/2'), which may be stretched by the pressure of the feces so that its central opening is everted through the vent. The urodeum and proctodeum (Fig. 37.22/3 and 4) are described with the urogenital system (p. 792).
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