Answer
15. Fetal blood flows through growths called chorionic villi which project into the placental sinus
Work Step by Step
Chorionic villi are projections from the walls of the chorion. Oxygen, and nutrients from maternal blood diffuse through the walls of the villi into the blood of capillaries of embryo or fetus. Carbon dioxide, and waste diffuse in the opposite direction, from fetal capillaries into villi, thence to maternal blood.
