The term area OA of Bonin refers to an area of the occipital lobe in the macaque defined on the basis of cytoarchitecture. It is located immediately anterior to area OB of Bonin. The cortical thickness is highly variable within and across subjects, and the boundary with area OB is very indistinct. In comparison to area OB, "About all one can say is that the cells of iiic grow smaller and there are fewer large cells in va." The anterior border with area PG of Bonin is distinguished by PG's greater thickness, reduced lamination, and increased cellularity of the internal pyramidal layer. Otherwise, the anterior boundaries of OA are indistinct ( Bonin-1947 ).