854 



THE INTESTINE. 



turned towards the vertebral column ; and it has accordingly been named 

 the arch of the colon. 



Above, the transverse colon is in contact with the under surface of the 

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

 end of the spleen. Below it are the convolutions of the small intestine, the 

 third portion of the duodenum being behind it. It is invested behind by the 

 general peritoneum, and in front it adheres to the sac of the omen turn. 



The DESCENDING COLON is continuous with the left extremity of the trans- 

 Terse colon by a sudden bend named the splenic flexure. It then descends 

 almost perpendicularly through the left hypochondriac and lumbar regions to 

 the left iliac fossa, where it ends in the sigmoid flexure. The peritoneum 

 affords a covering to it only in front and at the sides, whilst behind it is 

 connected by areolar tissue to the left crus of the diaphragm, the quadratus 

 lumborum, and the left kidney. It is usually concealed behind some convo- 

 lutions of the jejunum. 



The SIGMOID FLEXURE of the colon, situated in the left iliac fossa, consists 

 of a double bending of the intestine upon itself in the form of the letter S, 

 immediately before it becomes continuous with the rectum at the margin of 

 the pelvis opposite to the left sacro-iliac articulation. It is attached by a 

 distinct meso-colon to the iliac fossa, and is very movable. It is placed im- 

 mediately behind the anterior parietes, or is concealed only by a few turns 

 of the small intestine. The sigmoid flexure is the narrowest part of the 

 colon. 



Structure of tlie large intestine. The walls of the large intestine consist 

 of four coats, like those of the stomach and small intestine, namely, the 

 serous, muscular, areolar, and mucous. 



The serous and areolar coats require no further description here. 



The muscular coat, like that of the other parts of the intestinal canal, con- 



Fig. 599. 



Im 



Fig. 599. OUTLINE SKETCH OF A SEC- 

 TION OP THE ASCENDING COLON, f 



s, the serous or peritoneal covering ; 

 *', ', reflection of this at the attached 

 border forming a short wide mesentery, 

 between the folds of which the blood- 

 vessels are seen passing to the colon ; a, 

 one of the appendices epiploieae hanging 

 from the inner border ; Im, indicates at 

 the free border one of the three bands 

 formed by the thickening of the longi- 

 tudinal muscular coat; the dotted line 

 continued from the margins of these 

 bands represents the remainder of the 

 longitudinal muscular coat, and the 

 thick line within it, marked cm, repre- 

 sents the circular muscular layer ; m, 

 the mucous membrane at the flattened 

 part ; r, the crescentic bands or inden- 

 tations which divide the sacculi. 



sists of external longitudinal and 

 internal circular fibres. The longi- 

 tudinal fibres, though found in a 



certain amount all around the intestine, are, in the caecum and colon, 

 principally collected into three remarkable flat longitudinal bands. These 

 bands, sometimes called the ligaments of the colon, are about half an 



