the membranous structures that surround the embryo and contribute to the placenta and umbilical cord. They include the *amnion, *chorion, *allantois, and *yolk sac. In humans the allantois is always very small and by the end of pregnancy the amnion and chorion have fused into a single membrane and the yolk sac has disappeared.
The mucus-secreting skin that lines (and protects against the environment) all openings, cavities or entrances into the body, such as the intestinal tract, lungs, urinary tract, sinuses, vagina, etc.... mucous membranes (mucosa)
(exocoelom) 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.... extraembryonic coelom
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