yolk sac

views updated

yolk sac Membranous sac-like structure in the eggs of most animals. It attaches directly to the ventral surface or gut of the developing embryo in the eggs of birds, reptiles, and some fish, and contains yolk. The term also refers to an analogous sac-like membrane that develops below the mammalian embryo. It contains no yolk but is connected to the umbilical cord.

More From encyclopedia.com