The term area 25 of Walker refers to a subdivision of the frontal lobe of the macaque defined on the basis of cytoarchitecture. A narrow transition zone between area 24 of Brodmann-1905 (guenon) and area 10 of Walker, it has a "narrow but definite" internal granular layer (IV); the internal pyramidal layer (V) and multiform layer (VI) are narrow and undifferentiated as in area 24 of Brodmann. The molecular layer of the cerebral cortex (I), external granular layer (II) and external pyramidal layer (III) are similar to area 46 of Walker, but layer IV is thinner. Walker did not comment on the cytoarchitectonic homologue of this area in the human. It is topologically similar to area 32 of Brodmann (guenon) ( Walker-1940 ).