Abstract
The ampulla recti of mole in its proximal part being lined by a very thin wall, the nerve fibres running into it are very limited in number and both the AUERBACH's and the MEISSNER's plexus are very poorly developed, the ganglion cells in them being exceedingly scarce. In the more distal part of the ampulla, however, the muscularis as well as the submucosa become better developed and these formations attain the maximal development in the distalmost part of it. Therefore, in the last part the AUERBACH's plexus is powerfully formed and contains large ganglia, and smaller ganglia are otherwise found in the adventitia covered by the m. sphincter ani ext. of striated nature, The MEISSNER's plexus, however, remains rather ill developed here too.
The nerve fibres coming into the lower part of the rectum contain a considerable number of thick myelinated sensory fibres besides numerous fine vegetative fibres. The sensory fibres run through the plexus without coming into contact with the sympathetic ganglion cells and form their terminations in the submucosa or further up in the propria. The larger part of the terminations are of unbranched and simple branched type formed in the propria and most frequently in the connective tissue between the intestinal crypts. The terminal fibres are usually medium-sized and often show change in size in their gently winding courses. Besides, some uncapsulated simple glomerular terminations can be found on rare occasions.
The anal canal of mole extends very long. The proximal two-thirds of it constitutes the zona columnaris ani having longitudinal mucous folds, with both the columnae and the sinus covered under a noncornified stratified flat epithelium and well-developed papillae formed into it out of the propria. Far more numerous sensory fibres come into this zona columnaris than into the lower part of the rectum. Their terminations are of branched type. The terminal fibres show conspicuous change in size during their wavy or looped courses and usually end sharply over a wide terminal area. In this part, however, such intraepithelial fibres and sensory terminations in and near the periproctal glands as found abundantly in this part of man and some other mammals could never be found.
The distal one-third of the anal canal is the zona intermedia devoid of the longitudinal folds. The epithelium is here somewhat thinner than in the zone columnaris above and the papillae are worse developed. The mucous membrane here, however, contains a number of incoming sensory fibres forming branched terminations, which are, however, somewhat simpler in formation than those in the preceding zone. None of the terminal fibres form intraepithelial fibres here either.
The distalmost part of the anal canal forms the zona cutanea ani containing a few hair follicles and is followed by a patch of haired skin covering the anal canal and the lower part of the rectum. This skinny part contains a huge number of sensory fibres, perhaps accountable by the presence of circularly running smooth muscle fibres in the corium and the good development of the papillae from the stratum papillare into the epidermis, giving the skin of this part a close resemblance to that of the outer genitals. The fibres usually terminate in branched terminations and end bulbs formed by very thick sensory fibres. Of course the hair follicle necks are found to contain well-formed sensory terminations as usual.
The branched terminations in this part are found mostly beneath the epidermis. The branch fibres are large- or small-sized and show conspicuous change in size during their winding courses common to such fibres before ending in sharp points. Sometimes very many terminal fibres partake in forming rather complex branched terminations. On rarer occasions, the terminal fibres are found arranged in glomeruli.
