chorion

(ko'rt-on) [G. chorion, a skin.] The outermost of the fetal envelopes derived from the ovum. c. frondo's um [leafy c], the part of the chorion where the villi persist, forming the fetal part of the placenta, c. lae've [smooth c], the portion of the c. from which the villi have disappeared. prlm'itive c, the zona pellucid a in the stage of developing villi, shagg'y c, w. frondosum. smooth c, c. lasve.