CAVITY OF PELVIS. 225 



symphysis ; the capsule of the prostate is formed from 

 the lateral attachment to it of this fascia, which also 

 incloses the vesico-prostatic plexus of veins. It is this 

 portion of the pelvic fascia which it is so important to 

 avoid dividing posteriorly in the operation of lateral 

 lithotomy, for by so doing the urine would find its way 

 into the loose areolar tissue between the rectum and the 

 bladder. The presence of the prostatic plexus of veins 

 is often a serious source of danger. Posteriorly, the 

 pelvic fascia is continuous over the pyriformis muscle 

 and sacral plexus, being perforated by the internal iliac 

 artery and vein. 



The inlet of the pelvis is somewhat heart-shaped, well 

 padded along its upper border by the psoas and iliacus 

 muscles, while posteriorly, in the middle line, is the 

 promontory of the sacrum, or sacro-vertebral angle, 

 which can be readily felt through the abdominal parietes 

 in thin persons. Between the bladder and rectum is the 

 recto-vesical pouch, formed by the pelvic fascia, which 

 corresponds posteriorly where it is broad to the interval 

 between the iliac arteries ; it is narrow in front between 

 the rectum and the bladder, and extends as far as the 

 vesiculse seminales, and, in front and behind, to the tip 

 of the coccyx. Its relation to the orifice of the anus is 

 important, and must be referred to the condition of the 

 bladder, which, if distended, will raise the pouch further 

 into the pelvic cavity than its usual level, which is about 

 four inches above the anal aperture. Some coils of the 

 ileum and sigmoid flexure of the colon fill in the space. 

 The peritoneum affording no investment to the lower 

 end of the rectum, the neck, base, and anterior surface 

 of the bladder, or the front and inferior portion of the 

 posterior wall of the vagina, permits of operative pro- 



