allantois

allantois /al·lan·to·is/ (ah-lan´to-is) a ventral outgrowth of the embryos of reptiles, birds, and mammals. In humans, it is vestigial except that its blood vessels give rise to those of the umbilical cord.

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al·lan·to·is (-lnt-s)

n. pl. al·lan·to·i·des (ln-t-dz)

A membranous sac that develops from the posterior part of the alimentary canal in the embryos of mammals, birds, and reptiles, and is important in the formation of the umbilical cord and placenta in mammals. Also called allantoid.

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allan·toic (ln-tk) adj.

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allantois

a ventral outgrowth of the hindgut of the early embryo, which expands to form a large sac, filled with urine-like fluid, that fuses with the chorion to make up a major part of the placenta; vestigial in humans and some other species.

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allantois adenomatous dysplasia

adenomatous nodules and plaques on the allantois of mares; usually associated with fetal disease.