ExplanationThe prochordal plate is a circular, midline thickening of hypoblast cells that are firmly attached to the overlying epiblast cells. The plate eventually develops into a membrane called the oropharyngeal membrane at the site of the future mouth. It is interesting to note that at this early stage of development, the cranial versus caudal region of the embryo is established by the prochordal plate. And since the prochordal plate is located in the midline, bilateral symmetry is also established.
