The anatomy of the pericallosal arteries is described with emphasis on the areas supplied by the branches rather than the arteries themselves. Although variations are common, the blood supply to the paracentral lobule is quite constant and easy to see. An artery running up the marginal ramus is present in about 6o per cent of individuals and in many cases can be identified from its relation to the arteries in the central sulcus. Knowledge of the detailed anatomy of these vessels is especially helpful in the diagnosis of occlusive cerebrovascular disease.