The human pyramidal tract. XII. The effect of hemispherectomies on the fiber components of the pyramids

Probably every known neurological approach has been eniployed in efforts to locate the precise origin of the pyyamidal tract fibers. Among the various methods utilized are the following : Gross dissection ; normal anatomical and numerical studies of Retz-cells and pyramidal fibers ; secondary degenerative studies of cortico-spinal axons, myelin sheaths and “ boutons terminaux ” ; retrograde degeneration of pyramidal fibers and Betz-cells ; electrical stimulation of the cerebral cortex ; physiological defects following ablation experiments and finally the clinical and pathological effects of lesions in man. Almost all of the rescarcli done on this system in the last century has revolved around the central area of the cortex of tlie cerebrum. Very few investigators have taken into consideration the fact that the accepted definition merely states that the fibers of the pyramidal tract course through tlie pyramids of the medulla oblongata. Nothing in the wortling refers either to the origin or termination of the fibers. A survey of 114 years’ research in this field shows that many par ts of the enceplialon have been named as giving origin to the pyramidaltract fibers. The main regions, either singly or in combination, which have been designated, at one time or another, as sources are tlie following : motor cortex (area 4) ; premotor cortex (area 6) ; parietal cortex (areas I , 2, 3, 5 and 7 ) j the basal ganglia (lenticular nucleus or globus pallidus) ; and finally the brain-stem. The great majority of the investigations arc indicative of a more extensive origin than the so-called Betz-cell region of the motor cortex. Tiirck (1851) arid Swank ( ’36) have described fibers arising from the lenticular nucleus, tlie former in man and the latter in tlie rabbit. Those