Cloaca Subdivision

Left: A cloaca (asterisk) is being divided by a urorectal septum into, dorsally, a rectum-anal canal and, ventrally, a urogenital sinus. The urogenital sinus connects to the allantois and it receives mesonephric ducts. A ureter has branched off the mesonephric duct and is inducing kidney development. (Note: A cloaca persists in most vertebrates. It is present in birds, reptiles, amphibians, fish, and monotremes.)

Right: The urogenital sinus has given rise to the urinary bladder and urethra. A urachus connects the bladder to the allantoic cavity.

Below:Animation of a urorectal septum dividing the cloaca into a rectum-anal canal and a urogenital sinus. Growth of the ureter into the metanephrogenic mass is also animated.

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