The amnion and chorion are composed of extraembryonic ectoderm and mesoderm, whereas the yolk sac is composed of extraembryonic endoderm and mesoderm. By day 13, the connecting stalk, a dense portion of extraembryonic mesoderm, restrains the embryonic disc in the gestational sac.
The amnion and chorion are made of extraembryonic ectoderm and mesoderm, whereas the yolk sac is composed of extraembryonic endoderm and mesoderm. By day 13, the connecting stalk, a dense part of extraembryonic mesoderm, confines the embryonic disc within the gestational sac.