It has been suggested that this article be merged with Amnion. (Discuss) Proposed since August 2014.
The amnios is a pouch in which an embryo develops. It is a defining characteristic of amniotes. The amnios is adjacent to the epidermis, formed by the ectoderm of the fetus, and is extremely elastic.
In elephants, "The amnios is continued from the base of the umbilical cord upon the allantois, which is of considerable size, and is so interposed between the chorion and amnios, as to prevent any part of the amnios attaining the inner surface of the placenta. The amnios consists of two layers:one is the granular layer, continued upon the inner or foetal surface of the allantois, and thence upon the umbilical cord; the other is the smooth outer layer, continued upon the outer or chorional surface of the allantois, and thence upon the inner surface of the chorion.":348
^Owen, R. (1857). "Description of the foetal membranes and placenta of the elephant (Elephas Indicus, Cuv.), with remarks on the value of placentary characters in the classification of the mammalia". Philosophical Transactions of the Royal Society of London147: 347–353. doi:10.1098/rstl.1857.0017. JSTOR108622.
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