The coronary sinus -
High-Yield Explanation
Development of coronary sinus is from the body and left horn of sinus venosus. It lies in the posterior part of the coronary sulcus and drains into the right atrium. Though the besian veins/ venae cordis minimae drain directly into the right atrium, the the besian valves are guarding the opening of coronary sinus into the right atrium.