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Representative drawing of the early mammalian embryo during gastrulation. The internalization of the extraembryonic mesoderm (EM) during gastrulation allows for the creation of the intraembryonic mesoderm (IM) that could thus join functional amniotic and vitelline properties from the amnion (A) and yolk sac (YS), respectively. BI: blood islands; C: chorionic vellosities.
