ANUS. 



177 



deeply ; it is closely connected to the mucous 

 membrane, or the fine lining integument, and 

 appears a particular development of the circular 

 fibres of the intestine, like those which surround 

 the pyloric extremity of the stomach. This cir- 

 cular muscular ring consists of several fine and 

 pale fasciculi of fibres, which are closely con- 

 nected together, and when contracted form a 

 thick ring around the intestine immediately with- 

 in the anus; this muscle may be exposed either 

 by detaching the lining membrane which is but 

 loosely attached to it, or removing the rectum 

 from the subject, everting and distending it. 

 The mucous membrane being then detached, 

 the muscle will be distinct ; its upper border 

 is continuous with the circular fibres of the 

 rectum, and a distinct cellular line separates it 

 from the cutaneous sphincter ; anteriorly it is 

 connected with the levatores ani muscles. 



The action of this muscle must be to assist 

 the former sphincter in closing the lower ex- 

 tremity of the rectum and supporting its con- 

 tents ; in the process of defsecation it assists in 

 the expulsion of the residual portions of the 

 faecal matter, by the sudden or almost spas- 

 modic action which succeeds its relaxation ; 

 moreover, it strongly opposes the entrance of 

 any foreign body by the anus ; so that from 

 its power of resisting the ingress or egress of any 

 substance, it may be considered as constituting 

 a perfect pylorus. 



The subcutaneous adipose tissue in perineo 

 is very abundant in some situations; close to 

 the anus, or between the sphincter and the 

 skin, there is but very little ; hence abscesses 

 but seldom form there, except of very limited 

 size, such as small furunculi, or as the result of 

 circumscribed inflammation in some of the fol- 

 licles around the opening; whereas at either 

 side of the anus and rectum there always exists 

 a considerable quantity of cellular and adipose 

 matter, the former remarkable for the large 

 size of its cells, which are intersected by irre- 

 gular bands or fibres from the perinseal fascia, 

 and which give the whole some degree of 

 elasticity; the adipose substance is abundant, 

 very soft, loose, sometimes reddish, and fills 

 those large spaces which exist on either side of 

 the rectum. In no part of the body do ab- 

 scesses so frequently form as in these ischio- 

 rectal spaces ; and as such abscesses are very 

 generally attended with consequences tedious, 

 troublesome, and dangerous, it may be right 

 to make a few remarks on the anatomy of 

 these regions. 



Each Ischio-rectal space is a deep triangular 

 hollow, the base being situated towards the 

 integuments, the apex towards the cavity of 

 the pelvis ; the outer side is formed by the 

 ischium, and the inner by the rectum with 

 its muscles; this intestine, together with the 

 attachments of the levatores ani behind and 

 before, separates the two spaces from each 

 other, but the cellular membrane of one side 

 communicates with that of the opposite, and 

 hence in cases of diffused or extensive suppu- 

 rations, the fluid is occasionally observed to 

 pass from one side to the other; anteriorly 

 the transversus perinaei, and posteriorly the 



VOL. i. 



coccygeus muscles bound this hollow. Each 

 of these triangular recesses is lined on all sides, 

 except towards the skin, by fasciae, a view of 

 which may be obtained by dissecting out of 

 either all the contained adeps. There may 

 then be observed near the apex, or the deepest 

 part of the recess, a strong and tense aponeu- 

 rotic line, which is the inferior folded surface 

 of the pelvic fascia, which in this situation 

 sends off its inferior or descending layer ; 

 this latter immediately divides into two laminae, 

 an internal and an external ; the latter is called 

 the obturator, the former the ischio-rectal fascia; 

 the former is very strong and distinct, the latter 

 very thin and cellular. 



The obturator fascia descends a little ob- 

 liquely outwards and is inserted into the falci- 

 form process of the great sacro-sciatic liga- 

 ment, and into the tuberosity and ramus of the 

 ischium. It is very dense, being composed of 

 strong aponeurotic fibres, and it conceals and 

 separates from the perinaeum the obturator in- 

 ternus muscle, and the internal pudic nerves 

 and vessels, the perinaeal and hemorrhoidal 

 branches of which pierce it as they proceed 

 to their destination. The internal layer, or the 

 Ishio-rectal fascia, is much weaker and more 

 cellular than the last; from the before-men- 

 tioned aponeurotic line it descends obliquely 

 inwards along the lower and outer surface 

 of the levator ani as far as the sphincter, when 

 it becomes thin and cellular, and is lost in the 

 surrounding adipose tissue. Thus, by the 

 unfolding or division of the inferior layer of 

 the pelvic fascia into these two laminae, the 

 obturator and ischio-rectal fasciae, these re- 

 cesses are completely lined, and by the gradual 

 degeneration of the last named aponeurosis 

 into cellular and fibrous bands, which inter- 

 lace in every direction, the large mass of adi- 

 pose substance is enclosed and supported, whilst 

 a general firmness and elasticity is imparted 

 to the whole region. Towards the posterior 

 part of each of these regions a cul de sac is 

 enclosed between these fasciae and overlapped 

 by the glutaeus maximus, on the surface of 

 which the fasciae become extended, and ulti- 

 mately lost. A somewhat similar but smaller 

 cul de sac exists anteriorly behind each trans- 

 versus perinaei muscle. An inspection of the 

 Ischio-rectal spaces will serve to explain not 

 only the great size to which abscesses here 

 attain, but also the difficulty in effecting a cure 

 when they have been of long standing and of 

 considerable magnitude ; the constantly-vary- 

 ing form of the rectum on one side, the im- 

 moveable surface of the pelvis on the opposite, 

 a muscle above, and the integuments below, 

 all tend to prevent the possibility of effecting 

 any permanent apposition between the sides of 

 the cavity, while very generally the state of the 

 constitution is equally unfavourable to any 

 healthy action in the part. These several facts 

 have impressed surgeons with the propriety of 

 opening all such abscesses in a very early 

 stage, otherwise a large cavity will be formed, 

 the rectum denuded, and very frequently 

 opened by ulceration. 



Transversi perinai muscles ( Ischio-peri~ 



N 



