Noun has 2 senses

• yolk sac(n = noun.animal) umbilical vesicle, vesicula umbilicus, vitelline sac - membranous structure that functions as the circulatory system in mammalian embryos until the heart becomes functional;


• yolk sac(n = noun.animal) - membranous structure enclosing the yolk of eggs in birds, reptiles, marsupials, and some fishes; circulates nutrients to the developing embryo;