a histological comparison of myelinated nerve fibers between the external and extreme capsules in human brain

introduction: to recognize the myelinated nerve fibers of the external and extreme capsules in human brain. materials and methods: 10 adult and normal brains (20 hemispheres) from both sexes were studied using 15 mm serial secions in all three cardinal planes after fixation and processing. these sections were stained by klüver – barrera and heidenhin – woelcke methods. results: some fibers from different parts of the cortex through corona radiata entered the dorsal border of the external capsule, these fibers moved ventraly and ventrocaudaly toward the ventral border of the external capsule, and most of them entered the cerebral peduncles trans -, sub-, or retrolenticularly. some fibers passed through dorsal part of putamen and connected the external capsule with posterior limb of the internal capsule. some fibers passed between rostrum of corpus callosum and venteral part of the external capsule. some fibers traced from the external capsule to posterior bundle of the anterior commissure; some of them entered the commissure but others terminated in nucleus basalis (meynert) neurons. some fibers passed through rostral part of the external and extreme capsules.most of the fibers of the extreme capsule interconnected the temporal and frontoparietal operculi with the insular gyri, or with each other. a group of the extreme capsule fibers connected the adjacent insular gyri with each other. some fibers exchanged between the extreme capsule and the claustrum. there were fibers which went between the external and extreme capsules through the dorsal claustrum. conclusion: it is concluded that the external capsule contains all three groups of fibers, but it is mainly projectional; on the other hand, the extreme capsule is mainly associational. thus, in our opinion, these two capsules should be classified in different groups.