allantois

Noun
  1. The vascular fetal membrane that lies below the chorion and develops from the hindgut in many embryonic higher vertebrates (reptiles, birds and mammals) (synset 101476034)
    referred to in: mammal, mammalian - any warm-blooded vertebrate having the skin more or less covered with hair; young are born alive except for the small subclass of monotremes and nourished with milk
    is a type of: fetal membrane - any membrane that functions for the protection or nourishment or respiration or excretion of a developing fetus

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