Through the process of gastrulation, the bilaminar embryonic disc becomes trilaminar.

This means that two embryonic discs could only unite in locations where the ectoderm is absent.

The embryo proper and extramembryonic membranes are later derived from the embryonic disc.

Vasculature begins to develop in embryonic disc.

The embryonic disc now lies between the amniotic cavity and the primary yolk sac.

Through the process of neurulation, the notochord induces the formation of the neural tube in the embryonic disc.

After the 4th week of development, the growing embryonic disc becomes a great deal larger than the yolk sac and its presence usually dies out before birth.

The embryonic disc begins flat and round, but eventually elongates to have a wider cephalic part and narrow-shaped caudal end.

When day 13 rolls around, the connecting stalk, a dense portion of extraembryonic mesoderm, restrains the embryonic disc in the chorionic cavity.

Furthermore this secondary fusion of embryonic discs could implicate that intact skin will not fuse to other intact skin, including the ectoderm of the embryo.

The final two layers of the embryoblast are known collectively as the bilaminar embryonic disc as well as the bilaminar blastocyst or bilaminar blastoderm.

In monozygotic twinning for conjoined twins such as ischiopagi, the twins form by the splitting of a bi-laminar embryonic disc after the formation of the inner cell masses.

The inner cells will turn into the hypoblast layer that will surround the other layer called epiblast layer, and these layers will form the embryonic disc in which the embryo will develop.

Embryologists have traditionally attributed identical twinning as "splitting or fission" of either the inner cell mass of pleuripotential cells or early embryonic disc at 13-14 days of gestation just before the primitive streak.

The rest of the hypoblast and epiblast, not including the amnion, is what contributes to the bilaminar embryonic disc (bilaminar blastoderm/blastocyst), which sits between the amniotic cavity and the blastocyst cavity.

Moreover, the fusion occurs from neural folds of two separate, dorsally oriented embryonic discs, and the union can occur only after the ectoderm is disrupted to allow the neural and surface ectodermal layers to separate from each other.

The floor of the amniotic cavity is formed by the embryonic disk (or embryonic disc) composed of a layer of prismatic cells, the embryonic ectoderm, derived from the inner cell-mass and lying in apposition with the endoderm.