A nerve histological study was conducted on the experimental harelip suture operated on artificially prepared defects in upper lips of dogs. I. General Histological Findings Lining of the mucous epithelia was observed to occur slightly earlier than that of the dermal epithelia, although such time difference was negligible. In the primary stage of healing of the suture, there were deposits of blood clots intervening between the incised tissues, which were soon replaced by the granulation tissues leading to wound healing by the scar formation. There was not observed any hair root nor sebaceous gland regenerated in the scar tissue, except for some muscle fibers regenerated. II. Regeneration and Redistribution of Nerve Fibers By the 3rd day of operation, there was already observed in the blood clots as well as in the young granulation tissues development of immature blood vessels and redistribution of vegetative nerve fibers. Such an early appearance of vegetative nerve fibers in the blood clots before they turned into granulation tissues would suggest that the nerve fibers play an important role in conjunction with blood vessels in promoting healing of the wound. These vegetative nerve fibers, however, became decreased in number with lapse of time after the operation and the number of sensory nerve fibers became increased.
