extraembryonic coelom n the space between the chorion and amnion which in early stages is continuous with the coelom of the embryo proper
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the cavity, lined with mesoderm, that surrounds the embryo from the earliest stages of development. It communicates temporarily with the coelomic cavity within the embryo (peritoneal cavity). Late in pregnancy it becomes almost entirely obliterated by the growth of the amnion, which fuses with the chorion.
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the portion of the coelom external to the embryo, bordered by chorionic mesoderm and the mesoderm of the amnion and yolk sac; it communicates temporarily at the umbilicus with the intraembryonic coelom. Called also chorionic cavity and exocoelom.Medical dictionary. 2011.