Cloacae

Cloacae are the plural form of cloaca, a common posterior opening in certain animals through which the digestive, urinary, and reproductive tracts discharge their products. The term is used to describe both a single anatomical feature in a species and multiple instances across organisms.

In birds, many reptiles, and some other vertebrates, the cloaca is organized into three functional compartments: the coprodeum, which receives feces; the urodeum, which receives urine and the openings of the reproductive tract; and the proctodeum, which forms the vent for excretion. This arrangement allows a shared exit for multiple systems and can play a role in reproductive behavior, as in birds where cloacal contact accompanies mating.

Amphibians and monotremes also possess a cloaca, through which feces, urine, and, in males, reproductive fluids exit the body. By contrast, most mammals have evolved separate openings for the digestive and urogenital tracts, and the cloaca is either absent or greatly reduced, though vestigial remnants can occur in some taxa.

Clinically and in veterinary contexts, cloacal disorders—such as prolapse, infections, or congenital malformations—are important considerations for birds and reptiles. In comparative anatomy, the cloaca illustrates how diverse lineages have converged on a shared solution for integrating excretion and reproduction, while still showing notable variations across groups.

Etymology: cloaca derives from Latin, meaning sewer or drain; cloacae is its Latin plural.