The origin, course and termination of corticospinal fibers in the slow loris, Nycticebus coucang (boddaert)†

The origin and distribution of corticospinal fibers in the slow loris (Nycticebus coucang) were studied with the aid of the Nauta-Gygax technique following selected ablations of portions of the left cerebral cortex. Reconstruction of the cortical area which contributes to the corticospinal tract reveals a “motor” area which approximates that of Perodicticus, another lorisiform lemur, mapped by electrophysiological methods. Degenerated corticospinal fibers found in the contralateral lateral funiculus were traced caudally to sacral segments. A small number of degenerated fibers were also found in the ipsilateral lateral funiculus as far caudally as the lumbar cord. Preterminal fiber degeneration was most abundant in the contralateral dorsal horn and zona intermedia. Similar, but less abundant, degeneration was found in the contralateral ventral horn. Some degenerating fibers re-crossed through the dorsal and ventral gray commissures to the ipsilateral gray matter where preterminal fiber degeneration was most abundant in the medial portions of the ventral horn. Degenerating corticospinal fibers could be seen among the large, laterally-placed cells of the contralateral ventral horn.