External capsule

The external capsule is a thin sheet of white matter located between the putamen medially and the claustrum laterally. It is distinct from the internal capsule and contains mainly association fibres that contribute to connections between different regions of the cerebral cortex. Unlike the internal capsule, it is not a major pathway for corticospinal or thalamocortical projection fibres.

An important way to identify the external capsule is by its anatomical relationships. From medial to lateral, the structures are:

Putamen → external capsule → claustrum → extreme capsule → insular cortex

The external capsule is also a route for cholinergic fibres from the basal forebrain to the cerebral cortex. The capsule eventually joins the internal capsule around the lentiform nucleus.