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membranous structure that functions as the circulatory system in mammal embryos until the heart becomes functional

membranous structure that functions as the circulatory system in mammal embryos until the heart becomes functional

portion of yolk-sac of embryo bending from the umbilicus.

See Yolk-sac.

The navel sac, a structure of the human ovum which in the lower animals is called the vitelline sac or yolk sac. It is situated on the abdominal aspect of the embryo, being continuous with the omphalomesenteric duct. [Lat.]