The term area FDL of Bonin refers to an area of cerebral cortex defined on the basis of cytoarchitecture in the macaque. It is located on the medial surface of the frontal lobe where it occupies both walls of the cingulate sulcus. A part of area FD of Bonin, it differs little from the rest of area FD and the authors did not delineate it in their map of cortical areas. They regarded it as homologous to an area of similar structure and location described by Economo-1929 in the human ( Bonin-1947 ).