Answer:
The right atrium receives venous blood that comes from the body through the superior vena cava and inferior vena cava. The superior vena cava is formed by the union of the two branchiocephalic veins, it receives the blood that comes from the head, neck, upper members and the thorax.
The inferior vena cava is formed by the union of the two primitive iliac veins going up the retroperitonial space until reaching the right atrium, receiving venous blood from the lower members, abdomen and infradiaphragmatic vessels.
