The term prefrontal cortex (Walker) refers to the most rostral portion of the frontal lobe of the macaque "anterior to the arcuate sulcus on the lateral, ventral and medial surfaces of the lobe" ( Walker-1940 ). It includes eleven cytoarchitectural areas and parts of two others identified by Nissl stain. More than 40 specimens were cut in various planes to assure accurate measurement of cortical thickness. Observing that Brodmann-1909 and the Vogts-1919 had used different numbers to represent cytoarchitecturally equivalent areas in the macaque-like guenon and the human, Walker renamed several areas to coincide with the names Brodmann had given to equivalent areas in the human ( Brodmann-1909 ). Most investigators studying this region since the 1940s have based their terminology on that of Walker-1940. For more recent and more detailed segmentations based on multiple stains and connectivity in the macaque and the human see prefrontal cortex ( Carmichael-1994; Vogts-19192 ).