The term area FB of Bonin refers to an area of cerebral cortex defined on the basis of cytoarchitecture in the macaque. It was described as "thick agranular cortex without Betz cells in v" [the internal pyramidal layer]. The authors regarded area FB and area FBA of Bonin together as homologous to area FB in the human (as defined by Economo-1925). Certain features that distinguished area FB from area FA of Bonin in the human were less distinct or absent in the macaque, namely, the slight thinning of cortex, distinct border with FA, finer more radiate arrangement of cells, total absence of Betz cells, broadening of layer III [external pyramidal layer], and large cells in iii ( Bonin-1947 ).