Ventral motor nucleus of the cervical enlargement in some mammals; its specific afferents from the lower cord levels and cytoarchitecture

Abstract Specific projections from the lower spinal cord to the ventral motor nucleus of the cervical enlargement were studied in four mammalian species (cat, rabbit, dog and rat) with the Nauta and the Fink‐Heimer methods. Following hemisection of the lower spinal cord a medium amount of degeneration in laminae VII and VIII and scanty degeneration in the dorsolateral part of lamina IX were observed ipsilaterally at the levels from C6 to T2. In contrast, in all of these animals very dense and circumscribed degeneration was seen in a special ventral or ventrolateral cell group of lamina IX, designated here as ventral motor nucleus (VMN). Cytoarchitectonic study shows that this nucleus exists in the ventral or ventrolateral part of lamina IX from the caudal C7 to the rostral T1 segments, attaining the highest development in the C8 segment. Projections of short descending propriospinal fibers and dorsal root fibers to this nucleus were also studied in cats and rabbits. There was a small projection from a neighboring rostral segment, but no termination was found of dorsal root fibers. These results indicate that VMN in the C7 to the T1 segments is a special cell group which receives predominantly a strong projection from the lower cord levels of the same side.