Histological Study on the Innervation, Especially, Sensory Innervation of the Anus of Formosan Macaque

Abstract

The anus of Formosan macaque, as that of man, consists of the columnar, the intermediate and the cutaneous zones.In the columnar zone lacking in papillae growing out of the propria mucosae into the epithelium, the distribution of sensory nerve fibres is very scant, only a very small number of subepithelial unbranched or very simple branched terminations being found here. No intraepithelial fibres, as found in man and some other animals, could be found in this part of Formosan macaque.In the intermediate zone, the papillae being rather conspicuously developed, many sensory fibres are found coming in, their terminations comprising some unbranched and branched terminations as well as some genital nerve bodies. No intraepithelial fibres are to be found in this zone either.The genital nerve bodies may be classified into Type I and Type II. In a Type I genital body, 1 or 2 stem fibres running into the inner bulb rich in specific cell nuclei divide into several branches, sometimes coming into mutual anastomosis, and end in glomerular arrangement as a whole; most of these are capsulated and resemble the genital nerve bodies Type I found in the human anus (IZUMI) in form, but are smaller in size than the latter. The genital nerve bodies Type II are rather peculiar in form. The 1 or 2 sensory fibres running into the usually uncapsulated and dark-staining inner bulb end in a rather complex branched termination. The terminal fibres are thick, show frequent fibrillar expansions and change in size during their strongly winding courses and very often end swollen out into club-like tips, The zona cutanea ani is covered by a thick epidermis and well-developed papillae grow out of the corium into it. So, the papillary layer here is far better supplied with sensory fibres than in the common haired skin in other parts. These sensory fibres form, as in the intermediate zone above, unbranched and branched terminations as well as genital nerve bodies, mostly of Type I.The hair follicle necks of the zona cutanea ani are in a large majority completely hedged in by large-sized sebaceous glands and hair-nerve tubes inside them. Thus, the distribution of the sensory hair-nerve fibres here is plenty. Their terminations in most cases are of the fence-like type and only much less frequently of the plexus Type, no basket terminations as found in the pars cutanea of the lip of this animal being found in its anal skin. No PACINIan bodies could be found here either.