The occipital lobe of mammals is divided into three regions, each distinguished by a peculiar cytoarchitecture. In primates, the region which surrounds the calcarine fissure, the area striata, is characterized by an unusually broad band of medullated fibers, visible to the unaided eye, the stripe of Gennari.1 This stripe passes through the fourth cellular layer of the primary cortical center for sight. Surrounding the area striata lies the area parastriata (area 18 of Brodmann,2 OB of von Economo and Koskinas3), and around the area parastriata, the area peristriata (area 19 of Brodmann, OA of von Economo and Koskinas). The total depth of the cellular layers of these three divisions of the occipital lobe varies slightly, as follows: 2.41 mm. for area 17, 2.32 mm. for area 18 and 2.46 mm. for area 19. In Bolton's4 terminology, the granular layer, i. e. the fourth layer, makes up