The term area 46 of Walker refers to a subdivision of the frontal lobe of the macaque (Macaca) defined on the basis of cytoarchitecture. The first layer is wide, and the second and third layers are as wide or wider than the fifth and sixth layers. The third layer contains sparse, small pyramidal cells. The fourth layer, internal granular layer, is well developed and adjoins a layer of medium-sized pyramidal cells in the outer part of layer five. Walker regarded the most likely cytoarchitectural homologue in the human to be the middle frontal area 46 of Brodmann (human) ( Walker-1940 ).