<prompt> What is TRUE about sinus venosus:Forms rough wall of right atriumForms smooth wall of right atriumForms right coronary sinusForms left leaflet of coronary sinus  <response>: Sinus venosus is a paired structure but shifts towards right associating only with the right atrium as the embryonic hea develops. The left poion shrinks in size and eventually forms the coronary sinus and oblique vein of the left atrium, whereas the right pa becomes incorporated into the right atrium to form the sinus venarum smooth pa of right atrium. 