The term infraprincipal dimple refers to a small oblique depression variably present on the lateral surface of the frontal lobe of the macaques. It is located near the frontal pole ventral to the principal sulcus ( Krieg-1975; Paxinos-2009a ). Many macaques and humans have a much more prominent fronto-orbital sulcus located at about the same anterior-posterior level. Neither the dimple nor the sulcus has an equivalent in the smooth cerebral cortex of the rat or the mouse.