The lentiform nucleus (Latin for “lens-shaped”) includes the globus pallidus and putamen, which appear lens-shaped when viewed laterally. Both of these structures are lateral to the internal capsule, which separates them from the thalamus and caudate nucleus medially (eFig. 9.58). Laterally, the putamen is bordered by the external capsule, a thin layer of white matter adjacent to a thin gray-matter layer called the claustrum. Beyond the claustrum is the external capsule, which borders the white matter of the insula (eFig. 9.58).