epiboly

Epiboly is a biological term that describes the growth of one part over another. This process is particularly significant during gastrulation in embryonic development, where it involves the growth of the dorsal lip area. The term "epibolic" is an adjective used to describe processes or growth related to epiboly.12

In the context of animal development, particularly in reptiles, birds, and mammals with large amounts of yolk, the embryo forms from a disk of cells. This disk can split into an upper layer, the epiblast, and a lower layer, the hypoblast. Future mesodermal and endodermal cells migrate inward, with this migration often restricted to a specific area called the primitive streak. This process is a fundamental part of how embryonic cells differentiate and organize to form the structures of a developing organism.3