Chorion

(ko'-re-on). The outermost of the fetal membranes, formed from the external layer of the non-germinal epiblast. The chorion lies between the amnion and the deciduae (reflex a and vera). C., Cystic Degeneration of, a rare myxomatous disease of the chorion, producing the so-called " hydatid It is characterized by rapid increase in the size of the uterus, hemorrhage, often profuse, beginning during the second month of pregnancy, and the discharge of small whitish in appearance, surrounded by bloody clots. These vary in size from a pin's-head to a filbert. C. leve, the smooth or non-villous portion of the chorion. C, Primitive, the Vitelline membrane (or Zona pellucid a) during the time of the development of the hollow, structurele villi upon its surface. C, Shaggy, or C. frondosum, the part covered by villi.