Reciprocal point‐to‐point connections between parastriate and striate cortex in the squirrel monkey (Saimiri)

Abstract Experimental‐anatomical evidence is presented that in Saimiri two fiber systems project from area 18 upon area 17. Both systems terminate exclusively in layer I of area 17; in some other respects they exhibit characteristic differences. The fibers of the Horizontal System ascend from their origin in area 18 directly into layer I where they travel horizontally and parallel to each other to their termination site in area 17. This system is locally restricted since it connects only posterior area 18 with anterior area 17, i.e., it connects portions of both areas located near the representation line of the zero vertical meridian of the visual field. The fibers of the U‐fiber System arise from the supragranular layers of area 18. They reach their termination site in area 17 via the white matter from which they ascend perpendicularly into layer I. The U‐fiber system establishes a mirrorimage point‐to‐point connection between area 18 and area 17. This finding combined with the results of previous reports describing the similarly ordered association of area 17 with area 18 demonstrates a precisely organized reciprocal point‐to‐point connection between areas 17 and 18.