Any of the series of white matter fiber tracts in the brain that run between the most lateral segment of the lentiform nucleus and the claustrum; the white matter of the external capsule contains fibers known as corticocortical association fibers which are responsible for connecting the cerebral cortex to another cortical area; the capsule appears as a thin white sheet of white matter and provides a route for cholinergic fibers from the basal forebrain to the cerebral cortex; it eventually joins the internal capsule around the lentiform nucleus. [ MP:0020139 ]