Despite Considerable anatomical proof to the contrary, the myth of “end-artery” circulation to the brain has been perpetuated in textbooks for years. This interpretation of Cohnheim's original theory concerning infarction and his concept of end-arteries, published in 1872, has led to the erroneous assumption that cerebral collateral circulation is sparse and inefficient, if not actually nonexistent (1). The presence of a cerebral collateral circulation and its significance have become especially evident with our continuing angiographic evaluation of patients with stroke syndromes during the past three years (2). Our studies have prompted an evaluation of the importance of collateral circulation in these and other cases and an investigation of the pathways by which this occurs, as demonstrated on the cerebral angiogram. Normal Cerebral Blood Flow As far back as 1912, Kramer (3) demonstrated by means of dye injection in living animals that each internal carotid artery normally supplies blood only to the dis...