chorion

• The chorion is an outward skin which compasseth the child in the womb. —  The Works of Aristotle the Famous Philosopher Containing his Complete Masterpiece and Family Physician; his Experienced Midwife, his Book of Problems and his Remarks on Physiognomy
• It is only in some of the later Marsupials (Peramelida) and all the Placentals that the allantois develops into the distinctive and remarkable structure that we call the placenta The placenta is formed by the branches of the blood-vessels in the wall of the allantois growing into the hollow ectodermic tufts (villi) of the chorion, which run into corresponding depressions in the mucous membrane of the womb. —  The Evolution of Man — Volume 2
• As the connective tissue between the enlarged capillaries of the uterus disappears, wide cavities filled with maternal blood appear, and into these the chorion-villi of the embryo penetrate. —  The Evolution of Man — Volume 2
• In these Indecidua the villi are distributed over the whole surface of the chorion (or its greater part) either singly or in groups. —  The Evolution of Man — Volume 2
• Here again the whole surface of the chorion is thickly covered with the villi in the beginning. —  The Evolution of Man — Volume 2

Allen's Synonyms and Antonyms

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