embryonic disk

noun Embryology.

1. Also called embryonic shield. in the early embryo of mammals, the flattened inner cell mass that arises at the end of the blastocyst stage and from which the embryo begins to differentiate.
2. the blastodisk of yolky eggs.

n.

1. A platelike mass of cells in the blastocyst from which a mammalian embryo develops.embryonic shield
2. germinal disk