• PRACTICAL CONSIDERATIONS : THE LARGE INTESTINE. 1691 



Subcutaneous or submucous infection involving the anal canal may open into 

 the canal {incomplete internal fistula in ano), or upon the cutaneous surface just 

 without the margin of the anus {incomplete external fistula in ano), or in both direc- 

 tions {complete fistula in ano). 



It may begin with ulceration within the canal (most often, but not necessarily, 

 tuberculous), and may extend into the ischio-rectal fossa ; or it may originate in that 

 space, and, beginning as an ischio-rectal abscess, cause either of the abo\'e varieties of 

 fistula. Such abscesses are very frequent because of {a) the proximity of the rec- 

 tum, the frequency of rectal ulceration, and the invariably septic character of che 

 rectal contents ; {b) the poorly vascularized fat and loose connective tissue occupy- 

 ing the. fossa ; {c) the effect of gravity in inducing congestion ; {d) the absence of 

 muscles competent to facilitate the return of venous blood ; (<?) the slight but often 

 repeated trauma caused by coughing or straining, the ef?ect reaching the fossa 

 through the impact of the intestines on the levator ani, its roof ; {/) the exposure of 

 its contents to frequent slight external trauma, as in sitting on irregular surfaces, and 

 to marked changes of temperature. 



The anal fascia, the levator ani, and the strong recto- vesical fascia offer usually 

 a sufficient barrier to the progress of the abscess upward ; its outward extension is 

 limited by the obturator fascia, the obturator internus, and the tuberosity of the 

 ischium (Fig. 1426). Internally, below the level of the levator ani, usually about 12 

 mm. (% in.) above the anus, it finds its point of least resistance, and accordingly, 

 when it results in fistula, the internal opening will usually be found about on the line 

 between the sphincters, its higher exit from the fossa being prevented by the blend- 

 ing of the anal and recto-vesical fasciae and the levator ani muscle with the bowel- 

 wall. If it reaches the surface of the body, it will do so inferiorly in the space 

 between the anus and the tuberosity of the ischium and the edge of the gluteus maxi- 

 mus behind and the reflection of the deep perineal fascia in front (Fig. 1423). This 

 external opening is apt to be just beyond the outer margin of the external sphincter. 



Such abscesses should be opened early on account of the suffering caused by 

 pressure on the twigs of the small sciatic, the fourth sacral (on its way to supply the 

 external sphincter), the inferior hemorrhoidal and superficial perineal nerves, and 

 also to avoid the formation of fistula, and to forestall any possible extension upward 

 and a resulting pelvic cellnlitis from in\'olvement of the connective tissue between the 

 recto-vesical and pelvic fasciae and the peritoneum (Fig. 1425). They should be 

 opened widely to permit of perfect drainage, as the walls cannot definitely be ap- 

 proximated; the incision should be on a line radiating from the anus, so as to avoid 

 the hemorrhoidal vessels. In the presence of fistula following such an abscess, the 

 incision should unite the external and internal openings, and will usually divide the 

 external sphincter and the wall of the rectum. Incontinence of faeces does not per- 

 sist for any time, unless both sphincters are divided. The levator ani may aid in 

 preventing it (page 1692). 



In women free anterior division of the external sphincter may cause permanent 

 incontinence on account of the laxness of its anterior connections, the interposition 

 of the vagina preventing the firmer attachment to the pubes which in men is attained 

 through the medium of the triangular ligament. 



Fistula requires operation because drainage is imperfect and the region is acted 

 upon by the contractions of the levator ani, the muscular coat of the gut itself, and 

 by the external sphincter, the latter muscle being especially irritable and sometimes 

 hypertrophied. 



Cancer of the rectum may involve any portion, but is apt to be found within 

 two or three inches of the anus. In addition to the symptoms of obstruction, the pain 

 from contact of faeces with an ulcerated surface, and the blood which may streak the 

 stools, there are symptoms due to its anatomical surroundings which should be care- 

 fully studied. If it extends towards the hollow of the sacrum, it will press upon the 

 sacral plexus, causing pain which may suggest sciatica, lumbago, sacro-iliac disease, 

 or coxalgia. If it extends anteriorly, distressing vesical symptoms in the male may 

 distract attention from the real seat of the disease ; while in the female menstrual 

 derangement and suffering may have the same effect. Laterally it may involve the 

 ischio-rectal fossae, producing abscess and, later, multiple and intractable fistulae. 



