THE LARGE INTESTINE. 925 



peritoneum, and connected to the spine behind by a large and wide duplicature of 

 that membrane, the transverse mesocolon. It is in relation, by its upper surface, 

 with the liver and gall-bladder, the great curvature of the stomach, and the lower 

 end of the spleen ; by its under surface, with the small intestines ; by its anterior 

 surface, with the anterior layers of the great omentum and the abdominal parietes ; 

 its posterior surface on the right side is in relation with the second portion of the 

 duodenum, and on the left is in contact with some of the convolutions of the 

 jejunum and ileum. 



The descending colon passes downward through the left hypochondriac and 

 lumbar regions along the outer border of the left kidney. At the lower end of the 

 kidney it turns inward toward the outer border of the Psoas muscle, along which 

 it descends to the crest of the ilium, where it terminates in the sigmoid flexure. 

 At its commencement it is connected with the Diaphragm by a fold of peritoneum, 

 the phreno-colic ligament (see page 902). It is retained 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 and Transversalis muscles (Figs. 507, 508). It is smaller in 

 calibre and more deeply placed than the ascending colon, and is more frequently 

 covered with peritoneum on its posterior surface than the ascending colon (Treves). 



The sigmoid flexure 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 ending in the rectum at the brim of the true 

 pelvis opposite the left sacro-iliac symphysis. It curves in the first place forward, 

 downward, and inward for about two inches, and then forms a loop, which varies in 

 length and position, and which terminates in the rectum. 1 The first portion is in 

 close relation with the iliac fascia, and is covered by peritoneum on its sides and 

 anterior surface only. The loop is entirely surrounded by peritoneum, and is 

 retained in its place by a loose fold of peritoneum, the sigmoid mesocolon, which 

 connects it to the Psoas muscle. This loop, which normally hangs downward, 

 sometimes into the true pelvis, is very movable, and may be displaced upward in 

 cases of distention of the pelvic viscera. The sigmoid flexure is in relation in 

 front with the small intestines 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, to become continuous with the mesorectum near the 

 bifurcation of the common iliac artery (Fig. 490). In its left layer is the inter- 

 sigmoid fossa (see page 905). 



The rectum is the terminal part of the large intestine, and extends from the 

 sigmoid flexure to the anal orifice. The superior limit cannot be determined 

 precisely, since there is no point of demarcation between the sigmoid flexure and 

 the first part of the rectum ; but the brim of the true pelvis, opposite the left 

 sacro-iliac joint, is arbitrarily given as its point of commencement. From this 

 point it passes downward, backward, and to the right to the level of the third 

 sacral vertebra, where it lies in the middle line. This is the first part of the 

 rectum. The second part curves forward and is continued downward as far as the 

 apex of the prostate gland, about an inch in front of the tip of the coccyx. From 

 this point the bowel is directed backward, and, passing downward, terminates at 

 the anal orifice. This is the third portion of the rectum, or, as described by 

 Symington, the anal canal. It will be seen, therefore, that the rectum presents 

 two antero-posterior curves: the first, with its convexity backward, is due to the 

 conformation of the sacro-coccygeal column, and represents the arc of a circle, the 

 centre of which is opposite the third sacral vertebra. The lower one has its 

 convexity forward, and is angular. Its centre corresponds to a line drawn between 

 the anterior parts of the ischial tuberosities. Two lateral curves are also described : 



1 Treves describes the sigmoid flexure somewhat differently. He includes in his description of 

 this portion of the bowel the upper part of the rectum, and makes it terminate opposite the third 

 portion of the sacrum. Instead of forming a sigmoid curve, he describes it as a large loop or bend, 

 more like the Greek letter ft (omega). 



