The term area OFO of Roberts refers to a subdivision of the frontal lobe of the macaque (Macaca mulatta) defined on the basis of cytoarchitecture. The external granular layer (II) has densely packed granular cells; the external pyramidal layer (III) is narrow and sparsely populated with no large pyramidal cells; the internal granular layer (IV) is narrow but distinct; the internal pyramidal layer (V) has a dense population of small and medium pyramidal cells; the boundaries between layer V, the multiform layer (VI) and the subcortical white matter are indistinct. Area OFO "corresponds closely" to area 6b beta of Vogts ( Roberts-1963, Vogts-1919 ].