extra-embryonic membrane surrounding the embryo, amnion, and yolk sac, attached to the inner shell membrane; fusion of the chorion and allantois membranes about halfway through incubation; connected to the embryo via blood vessels to the heart through the abdominal wall; performs exchange of carbon dioxide from the embryo and oxygen from outside the shell, and collects wastes from the embryo; internal pip by the chick triggers its lungs and air sacs to begin functioning, the respiratory action of this membrane recedes and it dries up; it remains attached to the shell at hatch and disconnects from the chick at the umbilicus; if the shell is broken before the internal pip and this membrane is pierced, it can damage its blood vessels and interrupt its respiratory function before the chick’s lungs are ready to take over that function; abbreviated CAM