Ischio-rectal Fossa 437 



the pelvis, on account of a sheet of fascia which, coming from the 

 obturator fascia, slopes along the under surface of the levator ani to 

 the anus. This is the anal fascia. A stronger and much more 

 important layer of fascia also passes from the obturator fascia, over 

 the upper surface of the levator ani and the coccygeus, to lose itself 

 on the side of the rectum and bladder ; it is the recto-vesical fascia. 

 Behind the bowel the layers from the opposite sides of the pelvis 

 meet and invest the pyriformis and the sacral plexus, and between 

 the bladder and rectum the fascia invests the seminal vesicles. The 

 opposite sheets also form the lateral and anterior true ligaments 

 of the bladder, and also provide a special investment for the pro- 

 state and the prostatic plexus of veins. The most anterior part of this 

 recto-vesical fascia constitutes the pubo-prostatic ligament (p. 413). 

 The recto-vesical fascia helps the levator ani in preventing the abdo- 

 minal viscera sinking towards the ischio-rectal fossa ; it is at once a 

 sloping floor to the abdom n and roof to the fossa. In lateral lithotomy 

 the knife sometimes passes beyond the limit of the lobe of the prostate, 

 and, the ischio-rectal fossa being opened up into the pelvic cavity, 

 fatal cellulitis may occur. 



The presence of abundant loose tissue in the fossa allows the de- 

 scent and expansion of the rectum during defaecation ; it is through the 

 tissue at the front of the fossa that the surgeon cuts to reach the pro- 

 state and the neck of the bladder in lateral lithotomy (v. p. 443). As 

 the return of venous blood from this tissue is aided neither by the in- 

 fluence of gravity nor by active pressure of surrounding muscles, the 

 part is extremely liable to congestion and inflammation, and especially 

 so in the subject of feeble circulation, embarrassed respiration (phthisis), 

 or of advancing disease of the liver. Inflammation may also be set 

 up by a wet seat, or by injury. If the inflammation be followed by 

 suppuration, isciiio rectal abscess is the result. A common cause of 

 ischio-rectal abscess is the escape of a foreign body, such as a fish- 

 bone, or of some hard fasces, through the lateral wall of the bowel. 

 Such perforation of the bowel may be preceded by an ulcer, especially 

 in the case of stricture of the rectum or of tuberculosis. 



When suppuration occurs the abscess bulges at the side of the 

 anus, at the border of the gluteus maximus, or against the rectal wall. 

 In the last case there is great pain on defalcation, and on introducing 

 the finger into the bowel the fulness on its outer side is evident, and 

 perhaps fluctuation may thus be detected. In sitting the patient bears 

 all his weight on the opposite ischial tuberosity, resting upon the very 

 edge of the seat of the chair. 



If left to itself, the pus will find exit either into the rectum or 

 through the skin at the side of the anus ; the surgeon should open such 

 an abscess through the base of the fossa, making his incision in a line 

 radiating from the anus : that is, parallel with the haemorrhoidal vessels. 

 The sooner that he opens it, the less will be the resulting chasm. 



