The prefrontal granular cortex, with the premotor and motor areas, forms the frontal lobe. The three areas are allied by their proximity to one another and by their role in motor control. Of these three major subdivisions, the role of prefrontal cortex has been the most obscure. However, recent anatomical studies have elucidated the circuit basis for motor regulatory functions of the principal sulcus (Brodmann's area 9; Walker's area 46). In addition to well known and well worked out prominent connections with subcortical structures, e.g. the basal ganglia and deep layers of the superior colliculus, this area of prefrontal cortex is reciprocally connected to portions of the supplementary motor and premotor fields that are but one synapse removed from primary motor cortex. The principal sulcal cortex is additionally interconnected with the primary somatosensory area and the somatosensory association areas, in the frontoparietal operculum, with area PF of von Bonin and Bailey in the posterior parietal cortex, and with parts of the 'motor' thalamus. Recent behavioural and electrophysiological studies in monkeys (Macaca mulatta) demonstrate that the principal sulcus can influence delayed-responding, whether the response is a hand or an eye movement. The anatomical and functional evidence supports the thesis that prefrontal cortex has access to and can direct the output of several motor centres.