THE RECTUM 1307 



in position by the peritoneum, which covers its anterior surface and sides, its 

 posterior surface being connected by areolar tissue with the outer border of 

 the left kidney, and the Quadratus lumborum muscle (Fig. 988). It is smaller 

 in calibre and more deeply placed than the ascending colon, and is more fre- 

 quently covered with peritoneum on its posterior surface than the ascending 

 colon (Treves). 



The sigmoid flexure, pelvic colon, or sigmoid colon (colon sigmoideum) (Figs. 

 1047 and 1048) is the narrowest part of the colon; it is situated in the left iliac fossa, 

 commencing from the termination of the descending colon, at the margin of the 

 crest of the ilium, and then forming a loop, which varies in length and position, 

 and which terminates in the rectum at the level of the attachment of the mesen- 

 tery upon the front of the third sacral vertebra. It passes downward about 

 two inches (5 cm.) parallel to the outer border of the Psoas muscle, then taking a 

 transverse direction enters the cavity of the pelvis, crosses this cavity from left to 

 right and a little upward to the lower margin of the right iliac fossa; thence it 

 passes downward, backward, and inward along the anterior surface of the sacrum 

 to its junction with the rectum. It is surrounded by the peritoneum and is 

 attached to the posterior abdominal wall by the mesosigmoid. When the sigmoid 

 is lifted upward and to the right and the mesosigmoid is put slightly on the stretch 

 the intersigmoid fossa (p. 1268) is brought into view. When the sigmoid flexure 

 is empty most of it falls into the rectovesical or rectovaginal space (Fig. 1048). 

 When distended it mounts up into the abdomen, reaching to or even above the 

 umbilicus. The sigmoid flexure is in relation in front with the small intestine 

 and abdominal parietes. The sigmoid mesocolon is attached to a line running 

 downward and inward from the crest of the ilium, across the Psoas muscle 

 (Fig. 988). 



Applied Anatomy. The diameter of the large intestine gradually diminishes from the 

 cecum, which has the greatest diameter of any part of the bowel, to the point of junction of the 

 sigmoid flexure with the rectum, at or a little below which point stricture most commonly occurs 

 and diminishes in frequency as one proceeds upward to the cecum. When distended by some 

 obstruction low down, the outline of the large intestine can be defined throughout nearly the 

 whole of its course all, in fact, except the hepatic and splenic flexures, which are more deeply 

 placed; the distention is most obvious in the two flanks and on the 'front of the abdomen just 

 above the umbilicus. The cecum, however, is that portion of the bowel which is, of all, most 

 distended (see p. 1297). The hepatic flexure and the right extremity of the transverse coign are 

 in close relationship with the liver, and abscess of this viscus sometimes bursts into the gut in this 

 situation. The gall-bladder may become adherent to the colon, and gallstones may find their 

 way through into the gut, where they may become impacted or may be discharged per anum. 

 The mobility of the sigmoid flexure renders it more liable to become the seat of a volvulus or 

 twist than any other part of the intestine. It generally occurs in patients who have been the 

 subjects of habitual constipation, and in whom, therefore, the mesosigmoid is elongated. The 

 gut at this part being loaded with feces, from its weight falls over the gut below, and so gives 

 rise to the twist. 



The Rectum (Intestinum Rectum) (Figs. 1049, 1050). 



The rectum is continuous with the sigmoid flexure, while below it ends in the 

 anal canal. From its origin at the level of the third sacral vertebra it passes 

 downward, lying in the sacrococcygeal curve, and extends for about an inch (2.5 

 cm.) in front of, and a little below, the tip of the coccyx, as far as the apex of 

 the prostate gland. It then bends sharply backward to continue as the anal canal. 



It therefore presents two antero-posterior curves. An upper, with its convexity 

 backward, is due to the conformation of the sacrococcygeal column. The lower 

 one has its convexity forward, and is angular. Two lateral curves are also 

 described the one to the right, opposite the junction of the third and fourth sacral 



