The problem, which has consumed more than a year and a half in making preparations and studies, was undertaken at first with the hope of obtaining injections of individual arteries of the brain with an opaque substance that would show by means of the roentgen ray. Stereoscopic pictures thus taken could be studied, and the exact distribution of each cerebral artery traced throughout its entirety. It was soon found, however, that the Cohnheim theory of end arteries did not apply, at least to the cortex, to any marked degree. Though the original objective was not realized, the results of these studies have brought out other factors, which may be of interest and invite speculation. This paper will deal only, however, with four considerations: The degree and extent of end arteries in the brain. The degree and anastomosis existing between the larger groups of vessels. The relative vascularity in various portions