yolk sac

Noun
  1. Membranous structure that functions as the circulatory system in mammalian embryos until the heart becomes functional (synset 101467884)
    is a type of: sac - a structure resembling a bag in an animal
    same as: umbilical vesicle, vesicula umbilicus, vitelline sac
  2. Membranous structure enclosing the yolk of eggs in birds, reptiles, marsupials, and some fishes;
    Circulates nutrients to the developing embryo (synset 101467687)
    is a type of: sac - a structure resembling a bag in an animal

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