In the chick embryo, following delamination which separates the blastoderm into two layers, the epiblast is the upper layer of cells that contains the presumptive ectoderm, mesoderm and some endoderm. It is separated from the lower hypoblast.
In embryology, the epiblast is a class of cells present during gastrulation. It is one of two types of cells arising from the inner cell mass, but only epiblast cells give rise to the three germ layers of the embryo. Together, epiblast and hypoblast comprise the bilaminar disk of the developing embryo.