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one
of the four extraembryonic membranes of amniotes; it forms from the
somatopleure (ectoderm and somatic mesoderm). In birds and reptiles,
the membrane adheres to the shell and is highly vascularized to serve
in gas exchange. In mammals, it forms the fetal contribution to the
placenta, made by trophoblastic tissue and extraembryonic mesoderm,
containing blood vessels that allow exchange of materials with maternal
circulation. |
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