PRACTICAL CONSIDERATIONS : THE LARGE INTESTINE. 1687 



The sigmoid flexure, the most movable part of the large intestine, normally occu- 

 pies the pelvis rather than the iliac fossa (Fig. 1418), into which, however, it rises if dis- 

 placed by pelvic swellings or by a distended bladder or rectum, or if it is itself distended. 



From its shape and position and the relatively great length of its mesentery it is 

 very liable to assume unusual positions. It may be found on the right side of the 

 abdomen, may sink low in the pelvis (especially when loaded with faeces), and in 

 this latter position may, as a result of ulceration, adhesion, and perforation, open 

 into the bladder, the vagina, or even into the vas deferens (Allen), producing a 

 fecal fistula. 



Obstruction of the large intestine may be due to (i) fecal impaction. The 

 presence of the sacculi, the inspissation of intestinal contents, and the necessity for 

 overcoming gravity in the ascending colon, the left half of the transverse colon, and 

 the lower segment of the sigmoid curve favor the production of this condition. 



(2) Stricture is more common in the large intestine than in the small. It may be 

 (a) cicatricial and follow dysenteric ulceration in the rectum, sigmoid, or descending 

 colon ; tuberculous or stercoral ulceration in the ileo-caecal region ; or syphilitic or 

 tuberculous ulceration in the rectum ; or (b) malignant, most common as we ap- 

 proach the termination of the intestinal tract, so that rectum, sigmoid, descending 

 colon, hepatic flexure, splenic flexure, transverse colon, caecum, and ascending colon 

 represent the clinical order of frequency. The intimate relation of the hepatic 

 flexure to the gall-bladder subjects it to various forms of irritation, which probably 

 account for its relative susceptibility to malignant disease as compared with the 

 transverse colon ; while the mechanical conditions present in the caecum (page 1680) 

 apparently have a similar effect upon it, making it more frequently the seat of car- 

 cinoma than is the ascending colon. 



Malignant disease, in addition to producing stricture and obstruction, may ex- 

 tend into and involve any of the neighboring viscera. 



(3) Volvulus, in its usual form, is a twist of a portion of the bowel upon an axis 

 passing transversely through the affected segment of gut and its mesentery. In more 

 than two-thirds of all cases of volvulus the sigmoid loop is the part involved. The 

 usual cause is habitual constipation. The gut, becoming paretic from continued dis- 

 tention, hangs over into the pelvis and drags upon and lengthens the mesosigmoid. 

 Irregular contraction of the muscular layer of the gut in the effort to rid itself of the 

 fecal mass, or accumulation of faeces in one segment of the loop, so that it falls over 

 and descends below the other and less distended segment, may then cause the twist. 

 The immediate result is stoppage of the fecal current from the pressure of the two 

 ends of the loop on each other, and intense congestion of the whole loop from ob- 

 struction of the mesenteric vessels. Meteorism develops early and becomes exces- 

 sive as the entire intestinal tract is sooner or later involved in the distention. Vom- 

 iting appears late and is not very marked. The difference in this respect between a 

 volvulus of the sigmoid and an acute appendicitis (in which vomiting is often an early 

 and significant symptom) may be due to the fact that the nerve-supply of the former 

 is from the inferior mesenteric plexus, communicating directly with the aortic plexus 

 and only indirectly with the solar plexus. The region of the caecum and appendix, 

 like the small intestine, is supplied by the superior mesenteric plexus, having rela- 

 tion especially and directly to the solar plexus and to the right pneumogastric. In 

 volvulus of the small intestine vomiting is an early and persistent symptom. As well 

 known, for mechanical reasons and because of the greater fluidity of the intestinal 

 contents, vomiting is more apt to occur early and to be marked the higher the site 

 of an intestinal obstruction. 



The other forms of obstruction involving the large intestine foreign bodies, 

 bands, peritonitis, etc. have no especial anatomical significance. Intussusception 

 has already been mentioned. Hernia will be described later. 



The relations of the large intestine should be carefully studied (Fig. 1383) in 

 order to understand how (a) a renal, perinephric, or spinal abscess, or malignant 

 neoplasm of the kidney may open into, obstruct, or involve either the ascending or de- 

 scending colon; (^) a suppurating gall-bladder or an abscess of the liver may evacuate 

 into the beginning of the transverse colon; (<:) a gastro-colic fistula may become es- 

 tablished in cases of gastric ulcer involving the greater curvature; (d) an aneurism 



