Some connections of the entorhinal (area 28) and perirhinal (area 35) cortices of the rhesus monkey. II. Frontal lobe afferents.

In this investigation, the efferent cortico-cortical projections of the orbitofrontal cortex in the rhesus monkey have been investigated using silver impregnation methods. Projections from this area were observed to terminate in the rostral portions of the temporal lobe (areas TA, TE and TG) and cingulate gyrus (area 24), the insular cortex, and some dorsolateral prefrontal areas. Although these connections characterized all areas, with the exception of Walker's area 14 and Bonin and Bailey's area FL, the caudal levels of the orbitofrontal area were found to give rise to an additional projection which terminated in the entorhinal cortex and the transitional cortices bordering the rhinal sulcus. The source of this projection correlated closely with an area labeled FF by Bonin and Bailey. This connection may provide a much more direct means for the frontal lobe to influence the hippocampus than those involving the cingulate gyrus.