circulation: diagram showing course of circulation in the mammal. Blue represents unoxygenated blood; arrows indicate direction of flow. 1 capillaries of head, 2 pulmonary arteries, 3 pulmonary veins, 4 right auricle, 5 left auricle, 6,12 postcaval veins, 7 left ventricle, 8 right ventricle, 9 hepatic vein, 10 hepatic artery, 11 capillaries of the liver, 13 portal vein, 14 capillaries of digestive tract, 15 capillaries of kidney, 16 renal veins, 17 renal arteries