The term area FD delta of Bonin refers to an area of cerebral cortex defined on the basis of cytoarchitecture in the macaque. Located along the principal sulcus rostral to the arcuate sulcus, it is distinguished from area FD of Bonin in that the cells in layers other than the internal granular layer are smaller and "the usual dense va is much less obvious… ii and iii are unusually thick." The authors regarded it as the same as area 46 of Walker in the macaque and homologous to area FD delta of Economo in the human ( Bonin-1947 ).