The outermost membrane surrounding an embryo of a reptile, bird, or mammal. In mammals 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.’
Mid 16th century from Greek khorion.