The representation of the pyramidal tract in the internal capsule and basis pedunculi

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Abstract
This study was undertaken to elucidate the topography of the pyramidal tract of the internal capsule and basis pedunculi. Brain specimens from 3 verified cases of amyotrophic lateral sclerosis were topoanatomically examined, and the fibers were analyzed. In the horizontal section of the internal capsule, the changes were localized in the third region from the anterior end when the posterior limb was divided into 4 equal parts. In the basis pedunculi, the changes were also localized in the third region from the medial end when the basis pedunculi was divided into 4 equal parts. The changes in these regions were characterized by the absence of fibers with large caliber. The examination of the control brain specimen proved that the fibers with large caliber were distributed mainly in the regions previously described. It was concluded that the large fibers in the pyramidal tract, carried in bundles in the areas described, were chiefly degenerated in amyotrophic lateral sclerosis, and, hence, when the degenerating process extended into the internal capsule and basis pedunculi, the changes were localized in the areas previously described. Taking also into consideration the clinical manifestations and pathologic findings of the present cases of amyotrophic lateral sclerosis, it may be hypothetically assumed that the fibers with large caliber not only to the lower extremities but also to the upper extremities were carried in bundles chiefly through the third region of the posterior limb of the internal capsule and then in the corresponding region of the basis pedunculi. These large fibers are probably related with certain voluntary motor function and spasticity.

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