develops from develops from extraembryonic structure ectoderm extraembryonic ectoderm UBERON:0004366 Layer of the endoderm of the extraembryonic tissue. EMAPA:16065 we make the germ layer relationship develops_from, as currently the germ layers are declared to be purely embryonic. TODO - check. WP:Amnion - In the human embryo the earliest stages of the formation of the amnion have not been observed; in the youngest embryo which has been studied the amnion was already present as a closed sac, and appears in the inner cell-mass as a cavity. This cavity is roofed in by a single stratum of flattened, ectodermal cells, the amniotic ectoderm, and its floor consists of the prismatic ectoderm of the embryonic disk-the continuity between the roof and floor being established at the margin of the embryonic disk. Outside the amniotic ectoderm is a thin layer of mesoderm, which is continuous with that of the somatopleure and is connected by the body-stalk with the mesodermal lining of the chorion.