yolk sac

Definitions of yolk sac
  1. noun
    membranous structure enclosing the yolk of eggs in birds, reptiles, marsupials, and some fishes; circulates nutrients to the developing embryo
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    type of:
    sac
    a structure resembling a bag in an animal
  2. noun
    membranous structure that functions as the circulatory system in mammalian embryos until the heart becomes functional
    synonyms: umbilical vesicle, vesicula umbilicus, vitelline sac
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    type of:
    sac
    a structure resembling a bag in an animal
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