Lateral Fiber Dissection of the Central Core. A, The operculum over the insular surface was removed in this lateral view. The insula was also decorticated; the cortical gray matter of its surface was removed, revealing the thin extreme capsule underneath composed of short association fibers that interconnect adjacent insular gyri and the operculum. Note that the short and accessory insular gyri, at the anterior insular portion, will merge into the insular apex, and the long insular gyri will not reach this apex. B, The dissection is carried more deeply, removing the insular gyri and the extreme capsule. The claustrum is exposed and some major fiber tracts can be distinguished: the uncinate and inferior fronto-occipital fascicles, passing through the ventral claustrum, and the claustrocortical fibers arising from the dorsal claustrum. C, The claustrocortical fibers arise from the dorsal claustrum, and the removal of the former will lead to the removal of the latter, exposing the putamen underneath. Note that the uncinate and inferior fronto-occipital fascicles funnel together below the insular apex, a landmark that can be used to locate them under the insular surface. D, The uncinate and inferior fronto-occipital fascicles were removed and the lateral extension of the anterior commissure is seen. E, The putamen was removed and the globus pallidus is found at its medial and inferior aspect. The anterior commissure crosses the interhemispheric fissure, and as it progresses laterally, it passes at the inferior pole of the globus pallidus through Gratiollet’s canal and later underneath the ILS to reach the temporal lobe. The ventral striatum lies anterior and inferior to the anterior commissure. F, The globus pallidus was removed, exposing the entire internal capsule. Fibers from the internal capsule leave the central core as they continue to the cerebral lobes outside the outer limit of the putamen, becoming part of the corona radiata. The internal capsule is not present at the ventral striatum region (white star), making this region a continuous horizontal plate of loose gray matter that extends from lateral to medial along the basal forebrain until the septal area. (Images courtesy of E de Oliveira)