Nerve Supply of the Rectum and the Anus of Rabbit

Abstract

The nerve bundles coming into the caudal part of the rectum of rabbit contain nearly as many thick mednllated sensory fibres as in cat and dog but more of them than in man, besides far outnumbering vegetative fibres. These vegetative fibres come into close relation with the AUERBACH's and the MEISSNER's plexus, and end in terminal reticula (STOHR) as in all other organs and tissues. The ganglia in these plexuses are only very poorly developed, containing ganglion cells of merely infantile type. The sensory fibres run into the muscularis or the propria mucosae and end there in unbranched and simple branched terminations. The terminal fibres only very rarely ascend along the intestinal crypts but mostly end near their basis.In the anus of rabbit, the development of the smooth muscle layers being far worse than in the rectum, neither MEISSNER's nor AUERBACH's plexus could be found, but instead submucosal or proprial nerve plexus containing very numerous sensory fibres could be detected. Of these fibres, the enormously thick medullated fibres were often found, upon nearing the terminal area, to thin down abruptly and bifurcate at a RANVIER's node and the branches to repeat again such a bifurcation. Therefore, their terminal area is considerably extended. It is noteworthy that the stem as well as the branch fibres are abruptly thinned down just before and after the bifurcation at the RANVIER's node.In the mucous zone of the anus covered by a thick non-cornified stratified flat epithelium, the sensory terminations are always of branched type formed subepithelially, sometimes of complex type. The terminal fibres are often characterized by marked change in size and peculiar winding courses, but very rarely end intraepithelially. No glomerular bodies, as found in this part in man and other animals, could be found in rabbit.The zona cntanea ani of rabbit is far richer in sensory nerve fibres than the common haired skin. The sensory fibres ending in connection with the hair follicles here are comparatively scanty and their terminations are generally simple in construction. The numerous sensory fibres rnnning into the very thin stratum papillare usually end in branched terminatoins with rather many terminal branches, sometimes of very complex type. Not rarely terminal fibres which gave the impression of penetrating further into epidermis for a short way were also observed.