The term orbital sulci refers to superficial features of the ventral surface of the frontal lobe. In the human it is an H-shaped complex of intersecting grooves all of which are called simply 'orbital sulcus' ( Mai-1997; Ono-1990 ). Some authors refer to the groove forming the crossbar of the H as the transverse orbital sulcus ( Szikla-1977 ). The convolution between the legs of the H caudal to the transverse orbital sulcus is the posterior orbital gyrus; that rostral to the crossbar is the lateral orbital gyrus. About 60% of human have an unnamed sulcus extending from the transverse orbital sulcus rostrally toward the frontal pole ( Ono-1990 ). When that is present it adds an anterior orbital gyrus to the lateral orbital gyrus rostral to the transverse sulcus. The convolution medial to the H is the straight gyrus; that lateral to the H is the orbital part of the inferior frontal gyrus ( Mai-1997 ). In the macaque the ventral surface of the frontal lobe has two sulci, which correspond to the legs of the H in the human: the medial orbital sulcus and the lateral orbital sulcus. The convolution between them is the lateral orbital gyrus ( Martin-2000 ). Some have an intermediate orbital sulcus located between and parallel to the medial and lateral sulci ( Paxinos-2009a ). As in the human, the convolution medial to the medial orbital sulcus is the straight gyrus. The convolution lateral to it is the fronto-orbital gyrus. The macaque does not have a transverse orbital sulcus ( NeuroNames ). Equivalent structures are not found in the smooth cerebral cortex of the rat or mouse ( NeuroNames ).