The term area 9 of Walker refers to a subdivision of the frontal lobe of the macaque defined on the basis of cytoarchitecture. It is a somewhat heterogeneous area that differs from area 46 of Walker by an absence of radial striations, a narrower internal granular layer, and a less orderly arrangement of cells. On the surface facing the longitudinal fissure, the cortex is thinner and cells in the third layer are smaller than in area 46 of Walker. Walker regarded the most likely cytoarchitectural homologue in the human to be area 9 of Brodmann-1909 (human) ( Walker-1940 ).