#chorion  outermost membranous sac enclosing the embryo in higher vertebrates (reptiles; birds; mammals)
  supertype:  #sac  a structure resembling a bag in an animal
  part of:  #fetal_membrane
  part:  #chorionic_villus  one of the tiny villi that stick out of the fetal chorion and combine with the mother's uterine tissue to form the placenta

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