Figure 1.

Diagram (A) and schema (B) of the principles of organization of white matter fiber pathways emanating from the cerebral cortex. Long association fibers are seen end-on as the stippled area within the white matter of the gyrus. In their course, these fibers either remain confined to the white matter of the gyrus or travel deeper in the white matter of the hemisphere. Short association fibers, or U-fibers, link adjacent gyri. Neighborhood association fibers link nearby regions, usually within the same lobe. Striatal fibers intermingle with the association fibers early in their course, before coursing in the subcallosal fascicle of Muratoff or in the external capsule. Cord fibers segregate into commissural fibers that arise in cortical layers II and III, and the subcortical bundle, which further divides into fibers destined for thalamus arising from cortical layer VI, and those to brain stem and spinal cord in the pontine bundle arising from cortical layer V.²