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extraembryonic cells that, although derived from the zygote, are not part of the embryo proper and contribute to the fetal membranes (for example, amnion).
Synonym(s): primary mesoderm
Farlex Partner Medical Dictionary © Farlex 2012
Mesoderm lying outside the embryo proper and involved in the formation of amnion, chorion, yolk sac, and body stalk.
See also: mesoderm
Medical Dictionary, © 2009 Farlex and Partners