The claustrum, the external capsule and the extreme capsule of Macaca mulatta.

The claustrum is a sheet of gray matter situated between the putamen and the insular cortex. The external capsule borders the claustrum medially and separates it from the putamen. Interposed between the claustrum and the island is the extreme caps&. Xlost of the interest in the claustrum in past years has centered in ontogenetic and phylogenetic studies. No agreement has been reached amongst the various investigators as to its significance and much controversy still exists. At present, the knowledge of the fiber connections of the claustrum is incomplete. The ways in which the basal ganglia and the insular cortex are related to the claustrum and its surrounding capsulcs present interesting problems. One might speculate that the claustrum serves as :I relay in the discharge; directly or by way of the basal ganglia: from the supplementary motor areas of the cortex to the tegmc-ntum of the midbrain. The two capsules that bound the claustrum have also not been completely evaluated. There is no consensus regarding the functional significance or the fiber componeiits of the cxternal and the extreme capsules and the claustrum.