The term area FBA of Bonin refers to an area of cerebral cortex defined on the basis of cytoarchitecture in the macaque. Separated from area FB of Bonin by the spur of the arcuate sulcus (macaque) and bounded ventrally by the anterior subcentral sulcus, it is distinguished from area FB by 'larger cells in v [internal pyramidal layer], but usually not large enough to be called Betz cells". The authors regarded area FB and FBA together as homologous to the human area FB of Economo with distinctions described for area FB of Bonin ( Bonin-1947 ).