<Table> <Tr> <Td> </Td> <Td> This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations . Please help to improve this article by introducing more precise citations . (June 2015) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations . Please help to improve this article by introducing more precise citations . (June 2015) (Learn how and when to remove this template message) </Td> </Tr> <P> The coronary sinus is a collection of veins joined together to form a large vessel that collects blood from the heart muscle (myocardium). It delivers less - oxygenated blood to the right atrium, as do the superior and inferior vena cavae . It is present in all mammals, including humans . </P> <P> The name comes from the Latin "corona', meaning crown, since this vessel forms a partial circle around the heart . The coronary sinus drains into the right atrium, at the coronary sinus orifice, an opening between the inferior vena cava and the right atrioventricular orifice or tricuspid valve . It returns blood from the heart muscle, and is protected by a semicircular fold of the lining membrane of the auricle, the valve of coronary sinus (or valve of Thebesius). The sinus, before entering the atrium, is considerably dilated - nearly to the size of the end of the little finger . Its wall is partly muscular, and at its junction with the great cardiac vein is somewhat constricted and furnished with a valve, known as the valve of Vieussens consisting of two unequal segments . </P>

The great and small cardiac veins deliver their blood to what vessel