Definition of chorion in English:



  • The outermost membrane surrounding an embryo of a reptile, bird, or mammal. In mammals (including humans), it contributes to the formation of the placenta.

    ‘In insects, the genes that encode the proteins of the egg membrane, the chorion, become amplified in the surrounding follicle cells.’
    • ‘A needle was used to roll the embryo out of the chorion.’
    • ‘Care was exercised not to separate the amniotic sac into its components, the chorion and amnion.’
    • ‘Each embryo is surrounded, from exterior to interior, by the chorion, the vitelline membrane and the embryonic membrane.’
    • ‘Together with part of the chorion, these membranes make up the placenta, which physically attaches the embryo to the uterine wall of its mother.’



/ˈkôrēˌän/ /ˈkɔriˌɑn/


Mid 16th century from Greek khorion.