368 THE ABDOMEN AND PELVIS 



forwards to a point a little above the apex of the prostate, 

 where it bends sharply backwards and downwards, over the 

 anterior decussating fibres of the levatores ani, to form the anal 

 canal. The expanded lower part of the rectum is termed the 

 ampulla and is better marked in the female than in the male. 



In its upper third the rectum is clothed by peritoneum 

 anteriorly and on each side ; in its middle third it is only covered 

 anteriorly ; its lower third lies below the line of reflection of 

 the peritoneum from the rectum to the bladder (p. 357) and is 

 consequently devoid of any peritoneal covering (Fig. 115). 

 The upper two-thirds of the rectum is related anteriorly to the 

 coils of small intestine, or pelvic colon, which occupy the recto- 

 vesical fossa and separate it from the bladder, and tumours of 

 the pelvic colon may sometimes be palpated per rectum. In 

 front of the lower third of the rectum lie the seminal vesicles, 

 ductus deferentes and the prostate, embedded in visceral pelvic 

 fascia (Fig. 115). 



As it descends following the curvature of the sacrum and 

 coccyx, the rectum exhibits three lateral flexures , the uppermost 

 and lowermost being directed to the left and the middle one 

 to the right. As a result, the rectum is not median in position 

 but projects to the left side of the middle line. On the concavity 

 of each bend, a crescentic fold, consisting of the mucous and 

 circular muscular coats, projects within the lumen of the gut 

 and stretches almost halfway round it. These folds are known 

 as the plicce transversales recti (rectal valves), and they serve to 

 support the faeces and to prevent over-distension of the ampulla. 

 Scybalous masses supported by the lowest fold, which lies at 

 about three inches from the anus, can be reached by the tip 

 of the finger on rectal examination, but, as they cannot be 

 completely examined, care must be taken not to mistake them 

 for a malignant tumour. The plicae transversales recti can 

 easily be seen on examination with the sigmoidoscope when 

 the bowel has been artificially distended, but even then they 

 may tend to obstruct the passage of the instrument. 



Posteriorly, the upper two-thirds of the rectum is in contact 

 with the sacrum and coccyx in the median plane, and, on each 

 side, overlaps the piriformis muscle and the nerves of the sacral 

 plexus, from which, however, it is separated by the parietal 

 pelvic fascia and its own covering of visceral pelvic fascia. 

 When loaded, the rectum may exert pressure on the nerves, 

 especially of the left side, and produce the painful symptoms 



