allantois


al·lan·to·is

noun \ə-ˈlant-ə-wəs\
plural al·lan·to·ides \ˌal-ən-ˈtō-ə-ˌdēz, ˌal-ˌan-\

Definition of ALLANTOIS

: a vascular fetal membrane of reptiles, birds, or mammals that is formed as a pouch from the hindgut and that in placental mammals is intimately associated with the chorion in formation of the placenta

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