yolk sac Hear it!

yolk sac definition

yolk sac

  1. a saclike vascular membrane containing yolk, an outgrowth from the ventral surface of very yolky vertebrate embryos, as those of fishes, birds, or reptiles, that supplies nourishment to the embryo
  2. a homologous organ in most mammalian embryos that contains no yolk and that becomes a vestige at an early embryonic stage

Webster's New World College Dictionary Copyright © 2005 by Wiley Publishing, Inc., Cleveland, Ohio.
Used by arrangement with John Wiley & Sons, Inc.

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