EECTUM. 



1227 



is empty, and known as the pararectal fossa. As the rectum becomes distended 

 this fossa is encroached upon by the enlarging bowel, and soon is obliterated. 



The level at which the" reflection of the peritoneum takes place from the front of 

 the rectum is of considerable practical importance in connexion with operations in 

 this region. As a general rule that reflection, that is, the bottom of the recto- vesical 

 pouch, is placed at a distance of 1 inch (2 - 5 cm.) above the base of the prostate, or 

 about 3 inches above the anus, but the level is subject to considerable variation, 

 being as a rule relatively much higher in well-developed muscular or fatty subjects, 

 whilst in emaciated bodies, owing to the thinness of the structures forming the 

 pelvic floor, it is usually lowef. 



The bottom of the recto-vesical pouch may reach down in an extreme case to within an inch 

 (2'5 cm.) of the anus, whilst it is not at all rare to find it within 2 inches (5'0 cm.) of that orifice ; 

 on the other hand, it may be considerably higher than normal, sometimes being placed at a dis- 



Second sacral-vertebra 

 Sacro-iliac. joint 



Ending of pelvic mesocolon 



Sacral nerves 



Rectum 



Pararectal fo; 



Ureter (cut) 



Crescentic fold of 

 peritoneum (recto- 

 genital fold) 

 Seminal vesicle 

 beneath this 



Pararectal fossa 



Ureter (cut) 



Hypogastric artery 

 Obturator nerve 



Ureter 



Fossa 



obturatoria 



(Waldeyer) 



Inferior epigastric! artery 



Ureter 



Paravesical fossa 

 Plica vesicalis transversa 



Rectus 

 Pyramidalis 



Iliacus 



External iliac artery 

 Ductus deferens 

 Obliterated umbilical artery 

 Urinary bladder 



Median umbilical ligament (urachus) 



FIG. 961. THE PERITONEUM OF THE PELVIC CAVITY. 



The pelvis of a thin male subject, aged 60, was sawn across obliquely. Owing to the absence of fat the various 

 pelvic organs are visible through the peritoneum, though not quite so distinctly as presented here. 

 The urinary bladder and rectum are both empty and contracted ; the paravesical and pararectal fossae, as 

 a result, are very well marked. 



tance of 4 or 4^ inches (lO'O to 11-2 cm.) from the anus. It should also be added that the level is 

 generally believed to be somewhat raised by distension of the rectum and bladder, and lowered 

 when they are empty. 



In the child at birth, the peritoneum extends down to the base of the prostate (Symington), 

 and is thus lower in relation to the bladder ; but this may be partly accounted for by the high 

 position of this organ in the child. 



As a rule it will be found that 2 inches (5'0 cm.) of the front of the rectum, exclusive of the anal 

 canal, are entirely free from peritoneum, and it is this and the adjacent portion of the bowel which, 

 being free from the restraining influence of the peritoneum, is most distensible, and forms 

 the rectal ampulla. Including the anal canal, 3^ inches (87 cm.) of the rectum, measured along 

 the front of the tube, have no serous covering. On the other hand, the back is free from peri- 

 toneum for 5 or 6 inches (12'5 to 15'0 cm.) or sometimes much more above the anus. 



It is also of interest to notice th'at the connexion of the peritoneum to the rectum varies in 

 its character at different parts : Above and in front it is closely adherent, and can be removed 

 only with the greatest difficulty ; at the sides and inferiorly the connexion is much looser. As a 

 result, the peritoneum can be stripped off the rectum in its inferior third or half without much 

 .ifficulty, whilst in its superior portion this is not the case an arrangement which admits of the 

 free expansion of the rectal ampulla. 



