THORAX ABDOMEN AND PELVIS

Detailed explanation-1: -In type II (cardiac), the venous drainage flows directly into the right atrium or the coronary sinus. In type III (infracardiac), the pulmonary venous return reaches the right atrium by way of the inferior vena cava.

Detailed explanation-2: -The superior vena cava and inferior vena cava drain systemic venous blood into the posterior wall of the right atrium. The internal wall of the right atrium is composed of a smooth posterior portion (into which the vena cavae and coronary sinus drain) and a ridgelike, muscular anterior portion.

Detailed explanation-3: -The coronary sinus (from Latin corona ‘crown’) is the largest vein of the heart. It drains over half of the deoxygenated blood from the heart muscle into the right atrium.