The term area PrCO of Roberts refers to the part of the frontal operculum (OPRfr) in the macaque that belongs to the precentral gyrus (PFG). Topologically it is equivalent to the rostral part of ventral premotor cortex (PMVr). Identified on the basis of cytoarchitecture. It is thinner than the adjacent part of area 6 of Brodmann (guenon); the internal granular layer (IV) is more clearly distinguishable; the external pyramidal layer (III) is narrower with cells that are more sparse and lacking in size gradient; the internal pyramidal layer (V) has a dark band of densely packed medium and large pyramidal cells; and the multiform layer (VI) has two zones, the inner of which consists of small cells which "blend with subcortical white matter." Area PrCO may correspond to area 6b alpha of Vogts ( Roberts-1963; Vogts-1919 ).