What are extraembryonic membranes?
Are extraembryonic membranes the same among all vertebrates?
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Extraembryonic membranes are membranous structures that appear parallel to the embryo and which play important roles in embryonic development. They form from the embryo but do not become part of the individual organism after its birth.
The extraembryonic membranes that may be present in vertebrates are the yolk sac, the amnion, the chorion, the allantois and the placenta.
The presence of each extraembryonic membrane varies according to the vertebrate class.
In fish and amphibians, only the yolk sac is present. In reptiles and birds, in addition to the yolk sac, the amnion, the chorion and the allantois are also present. In placental mammals, in addition to all these membranes, the placenta is also present.
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