1. A temporary membrane formed during embryonic development in birds and reptiles, consisting of the fused chorion and allantois, that functions in gas exchange and nutrient absorption.
Usage: embryology; biology; technical term

Examples

• The chorioallantois develops early in avian embryos and becomes the primary respiratory organ.
• In chicken eggs, the chorioallantois lies just beneath the shell membrane.
• The chorioallantois allows oxygen to diffuse from the air cell into the developing embryo.
• Researchers studied the vascularization of the chorioallantois to understand embryonic development.
• The chorioallantois eventually degenerates after the chick hatches.