White matter of the external capsule and claustrum.  In this lateral perspective of the right cerebrum, the cerebral cortices have been dissected to reveal some of the deep white matter tracts. At the top of the figure are seen a few short associational fiber bundles known as arcuate fibers (not to be confused with the arcuate fasciculus).  Arcuate fibers are U-shaped collections of corticocortical axons that connect adjacent gyri with one another.  The external capsule is a sheet of white located between the putamen medially and the claustrum laterally.  It contains mainly corticocortical association fibers, including the inferior fronto-occipital fasciculus and the uncinate fasciculus.  The claustrum, only partly visible in this dissection, is a thin sheet of gray matter that lies lateral to the external capsule and deep to the insula.  It has extensive and reciprocal interconnections with widespread areas of the ipsilateral cerebral cortex; however, it function remains enigmatic.  The inferior part of the optic radiation projects from the lateral geniculate nucleus of the thalmus into the temporal lobe as Meyer's loop. The fibers then loops posteriorly, lateral to the inferior horn of the lateral ventricle, to reach the primary visual cortex on the medial surface of the occipital pole. (Image courtesy of PA Rubino)