180 



ANUS. 



the parietes of the lower extremity of the in- 

 testine ; these are the longitudinal muscular 

 fibres, the mucous membrane, and the sub- 

 mucous cellular tissue. The longitudinal fibres 

 of the alimentary tube exist through its whole 

 extent, but like the circular are differently mo- 

 dified in different situations; thus along the oeso- 

 phagus they are very fully developed, also along 

 the arches of the stomach; in both these situa- 

 tions the fibres are strong and somewhat red ; 

 whereas on the parietes of the small intestines 

 they are very indistinct and pale ; on the coecum 

 and colon they are still pale, but very distinct, 

 being collected into three flat fasciculi or bands. 

 On the rectum, as on the oesophagus, they are 

 again fully developed as to thickness and num- 

 ber ; their colour is still rather pale. In the 

 two superior thirds of this intestine, or as low 

 down as the prostate gland, they predominate 

 over the circular fibres, which are internal, 

 whereas in the lower third the latter prevail; 

 the former terminate, some by becoming con- 

 tinuous or intermingled with the fibres of the 

 levatores ani, others with the cutaneous sphinc- 

 ter so low as the border of the anus, and some 

 are inserted into the submucous tissue of the 

 intestine ; these fibres are continuous superiorly 

 With those of the colon ; they serve to continue 

 that successive series of contractions or shorten- 

 ings of the intestine, which essentially assist in 

 the process of defaecation. As the longitudinal 

 fibres of the rectum resemble those of the oeso- 

 phagus, so the inferior circular fasciculi or the 

 sphincters are like the muscles of the pharynx, 

 not merely in their increased strength and colour, 

 but also in their vital power. Over the lon- 

 gitudinal fibres the will lias no control, whereas 

 the inferior circular are to a certain extent under 

 its influence. Here, then, as in the organs of 

 deglutition, we perceive the animal and organic 

 powers still distinct as to their elementary na- 

 ture, but becoming intimately, nay inseparably 

 associated for wise and obvious purposes. 



In the act of defaecation the offices of the se- 

 veral muscles connected with the anus may be 

 summed up as follows : When the contents 

 of the rectum, particularly if of a solid con- 

 sistence, are being expelled, the whole rectum 

 descends, and the perinaeum becomes promi- 

 nent in consequence of the viscera being forced 

 against it by the contraction of the diaphragm 

 and abdominal muscles. The presence of the 

 faeces irritates the muscular fibres of the rectum; 

 the longitudinal fibres shorten the intestine, 

 while the successive actions of the circular 

 urge down the faecal mass; these two orders 

 of muscular fibres are the true antagonists to 

 the sphincters. During this stage, however, 

 the sphincters are relaxed, and the anus be- 

 comes dilated, partly by the contents of the rec- 

 tum distending it, ana partly by the levatores 

 ani muscles, which are nevertheless in a suffi- 

 ciently relaxed condition to allow the protru- 

 sion of the rectum and anus, while they still 

 support the latter to a certain extent, and thus 

 exert a sort of check against its forcible de- 

 scent ; they also tend to open the orifice of 

 the anus. During this forcible expulsion, a 

 small portion of the mucous lining is frequently 



protruded. The expulsion of the last portion 

 of faeculent matter is then effected by the sub- 

 sequent strong and gradual contraction of the 

 levatores ani compressing the rectal pouch, and 

 raising the rectum and anus to their former 

 position, and lastly, the sudden action of the 

 sphincters clears and closes the orifice. 



The mucous membrane lining the rectum is 

 in every respect highly organized, it is thrown 

 into several folds, and is larger and looser 

 than the other coats, hence portions can be 

 easily removed by operation, and are not 

 unfrequently detached by gangrene. As it 

 approaches the anus, it is very red, soft, and 

 fungous, being highly vascular, presenting the 

 orifices of several glands, follicles, or lacunas. 

 It is here very loosely connected to the muscu- 

 lar fibres, and is frequently found thrown into 

 irregular folds ; these are protruded somewhat 

 during defaecation, and when morbidly enlarged 

 or thickened, are not unfrequently the source 

 of considerable pain and inconvenience. As the 

 mucous membrane is not contractile, these folds 

 are necessarily increased when the longitudinal 

 fibres of the rectum contract and shorten the 

 intestine; they are then protruded together 

 with the faecal matter. Immediately above the 

 plaited margin of the anus the skin and mu- 

 cous membrane become continuous ; the ter- 

 mination of the cuticle appears rather abrupt, 

 just within the internal sphincter. Some de- 

 scribe it as continued higher up, and gradually 

 lost on the surface. I have not been able to 

 exhibit it satisfactorily higher than the point 

 indicated, nor does it appear to me that it 

 extends through this orifice by any means to 

 the same extent as through the other outlets 

 of the body, the mouth, nose, urethra, or va- 

 gina. In the latter passage in particular 'it 

 is very distinct, even in health ; and in disease, 

 as in cases of prolapsus uteri, its develop- 

 ment becomes considerable; whereas in pro- 

 lapsus ani, that is, a protrusion of the mucous 

 lining of the rectum, at a little distance above 

 the anus, I have not found the protruded 

 mass to become covered with cuticle : I have 

 seen cases of long standing in which the surface 

 presented the same soft, vascular tissue as it 

 does at first. It does not controvert this state- 

 ment to find tumours about the margin of the 

 anus (hemorrhoids or polypi) covered with a 

 thickened or developed cuticle; for in such 

 cases the cutaneous covering is derived from 

 the elongation of the surrounding skin, which 

 has increased in density from exposure to the 

 air, and from continued irritation. The same 

 remark will apply to cases of artificial anus, 

 no matter in what situation : in all these the 

 villous surface, which protrudes during the 

 peristaltic acton, retains its mucous charac- 

 ters, and does not become covered with cu- 

 ticle. From these facts it may be inferred 

 that cuticle is never developed in any situation 

 in which it did not originally exist, but that 

 circumstances favour the increase or more full 

 development of it in those situations where it 

 naturally occurs, even though its normal con- 

 dition be extremely delicate and fine. 



nd vessels. The submucous tissue 



