Neurohistological studies were performed at the anus by using BIELSCHOWSKY-SUZUKI'S silver impregnation method.
The most of nerve fibers entered into the external sphincter at the upper half part of sphincter muscle. In the muscle layer nerve bundles branched and spreaded arborescently from outside to inside, while they descended from upper outer portion to lower inner portion like staircase. A small part of nerve fibers innervated the sphincter muscle making the motor end plates, but a large part of nerve fibers left the external sphincter from the lower end of superficial external sphincter for intersphincteric connective tissue, then passed under the internal sphincter and went upward.
The motor end plates, the only nerve endings in the external sphincter, were rich in the lower two third of the sphincter, and numerous in the newborn but very few in the other age. Untill 6 month of age the motor end plates were found in groups, but becoming older they were scatterd. The structure of motor end plate of the external sphincter was very simple and its differentiation was less advanced than that of skeletal muscle.
The nerve fibers appeared almost mature in the form after 6 month of age.

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The nerve supply of the intersphincteric tissue had two origins.
The first was the extrinsic nerve fibers coming from the pelvic space as the thick bundles which had no nerve cells, while descending outside of the longitudinal muscle they sent many branches toward the longitudinal muscle, especially the connective tissue inside of the longitudinal muscle where intrinsic AUERBACH'S ganglions were not present. Argyrophobe thin fibers in the extrinsic nerve, mainly distributing upper part of this layer, were considered as the autonomic nerve fibers. It was unlikely that argyrophil thick fibers in the extrinsic nerve, which mainly found in the lower part, made terminations.
The second was intrinsic AUERBACH'S plexus. Plexus and ganglions tended to disappear more orally in older subjects, and not to be found after 6 month of age. There were no matured ganglion cells in the newborn. In the anal canal, the ganglions were larger and fewer, and nerve networks of the plexus were larger and irregular than those of the rectum. Around the site where ganglions disappear nerve bundles located between ganglions became very thick, and descending the agangionic region appeared to be free end in the terminations.

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Hara has examined 500 consequtive autopsy specimens of the colon in over 50 years of age in Japan and Matsumura has examined 121 consequtive autopsy colon specimens in Germany. The findings of the histological examinations were compared and following conclusions were obtained:
1. The frequency of colonic polyps was high with increasing age.
2. There was no definite difference about the frequency of colonic polyps in Japan and Germany over 50 years of age. Namely one in three to four examples over 50 years had approximately one to three tiny polyps in their colon.
3. It seems that in Japan one finds polyps in the right half colon then in the left. Cancer incidence is also higher in the right half colon. The findings suggest that there could be some relationship between these two kinds of tumors of the colon.
4. Diverticulosis was also examined. The frequency in Germany was four times higher than that in Japan.

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