yolk sac

1 definition found

yolk sac - WordNet (r) 2.1 (2005) :

  yolk sac
      n 1: membranous structure that functions as the circulatory
           system in mammalian embryos until the heart becomes
           functional [syn: yolk sac, vitelline sac, umbilical vesicle
           , vesicula umbilicus]
      2: membranous structure enclosing the yolk of eggs in birds,
         reptiles, marsupials, and some fishes; circulates nutrients
         to the developing embryo