Sural--lateral plantar nerve communications in Japanese macaque.

It is generally accepted that the sural nerve in humans contains exclusively sensory and autonomic fibers. Recently, however, a few clinical reports have suggested that the human sural nerve contains motor fibers. On the other hand, it is known that motor fibers are present in the sural nerve of rats and dogs, and that the fibers reach intrinsic muscles of the foot via a communicating branch to the lateral plantar nerve. The author investigated the communicating branch between the sural and lateral plantar nerves in Japanese macaques, and examined both nerves by the fiber analysis method, removing the perineurium under a stereoscopic microscope. The communicating branch was found in all examined macaques. Nerve fibers which derived from the sural nerve via the branch reached the abductor digiti quinti, the flexor digiti quinti brevis, the contrahentes digitorum, the adductor hallucis, the interosseous and the lumbrical muscles. Furthermore, these fibers supplied the lateral part of the skin of the sole and the metatarsophalangeal joints. These findings in the Japanese macaques suggest that we may encounter the communicating branch between the sural and lateral plantar nerves in other primates including humans as in rats and dogs.