Extra-embryonic cavities

The embryo completely penetrates the uterine endometrium and eventually becomes completely embedded in it (Implantation, S5). The amniotic cavity arises on the dorsal side of the embryoblast, and the primary umbilical vesicle arises on the ventral side. Once the secondary umbilical vesicle has developed from the primary vesicle, a third extra-embryonic cavity is formed: the chorionic cavity.