Medial portions of the left hemisphere have been removed to reveal systems of fibers in the medullary substance. In addition to short association fibers (arcuate fibers) the broken ends of longer association fibers and projection fibers are seen extending upward into the field of dissection. The sulcus cinguli (6), which contains a branch of the anterior cerebral artery, has been exposed to its depth by the removal of part of the left superior frontal gyrus, the medial portions of the precentral and postcentral gyri and the paracentral lobule (of the medial aspect of the hemisphere). The upper surface of the gyrus cinguli is thus exposed. Further posteriorly resection of the superior parietal lobule and precuneus has exposed the depths of the left parieto-occipital fissure and its contained branches of the posterior cerebral artery. The dissected area extends laterally to the interparietal sulcus and superior frontal sulcus. Comparison should be made with the intact right hemisphere.