chorion

(ko’re-on) (Gr. χόριον skin). external of the two fetal membranes, formed by the outer portion of the allantois pushing in between the amnion and vitelline membrane, and uniting with the latter to envelop the ovum. c. frondo’sum, the part of the chorion that is covered with villi. c. lsa’ve, the smooth and membranous part of the chorion. primitive c., that stage of the zona pellucid a during which it develops many small villi. shaggy c. Same as c. frondosum.