bilaminar disc

A flattened, almost circular bilaminar plate of cells formed when the inner cell mass (aka embryoblast) forms two epithelial layers, each of a distinct lineage, separated by an extracellular basement membrane: the external (dorsal) layer is called the epiblast and the internal (ventral) layer is called the hypoblast (aka primitive endoderm); together, they compose the bilaminar embryonic disc.