Veins drain into the vesical and then internal iliac veins. People with varicose veins are more often affected. These can originate in veins or arteries. They receive blood from the paired renal arteries; blood exits into the paired renal veins. This is the same procedure used to treat varicose veins and similar disorders. Thrombi form more frequently in arteries than veins. Praxagoras identified the difference between arteries and veins. This is achieved by the coronary circulation, which includes arteries, veins, and lymphatic vessels. Nothing is mentioned about veins or arteries. The sigmoid drains into the large internal jugular veins. Capillaries merge into venules, which merge into veins. Erasistratus was among the first to distinguish between veins and arteries. Most variations are due to coughing or internal compression of jugular veins in the neck. Most of the blood of the coronary veins returns through the coronary sinus. Blood must be drained from the veins.