Leg muscles of the monkey have been studied following partial denervation produced by surgical elimination of from 25 to 90 per cent of the axons entering the sciatic nerve from the lumbosacral plexus. The investigation included observations on function, rate and degree of muscle atrophy, and neurohistological appearance of the affected muscles.

In most of the cases, from 83 to 90 per cent of the residual nerve fibers in the peroneal and tibial nerves were destroyed and a severe paresis of the leg muscles was produced. No functional improvement was noted up to 160 days after operation, and the affected muscles became markedly atrophic. Histological examination of these muscles failed to reveal more than sporadic collateral regeneration of the residual axons.

In two cases 50 and 75 per cent of the peroneal and tibial nerve fibers remained intact 63 and 200 days, respectively, after operation. The legs operated upon in these cases functioned almost normally and all muscles weighed within 11 per cent of those of the contralateral, normal leg. Histological study and counts of end-plate: nerve fiber ratios showed that many residual axons had regenerated collateral branches which entered denervated end-plates. Collateral regeneration was incomplete, however, and many end-plates remained without innervation.

These results indicate that residual axons in paretic muscles of a primate do not regenerate collaterally as readily as do those of other previously studied mammals.

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