1028 THE ORGANS OF DIGESTION. 



bends to the left, and takes a transverse somewhat ascending course to the spleen. 

 In the left hypochondrium it bends again and descends along the left posterior 

 abdominal wall to the left iliac fossa, then becomes convoluted as the sigmoid 

 flexure : it finally enters the pelvis and descends as the rectum along its posterior 

 wall to the anus. 



There are to be distinguished, then : 



1. Caecum (intestinum caecum), or Caput coli ; 



2. Colon ascendens, or Right colon ; 



3. Hepatic flexure, or Flexura coli dextra ; 



4. Colon transversum ; 



5. Splenic flexure, or Flexura coli sinistra ; 



6. Colon descendens, or Left colon ; 



7. Flexura sigmoidea (Colon sigmoideum), or S. romanum. 



8. Rectum (intestinum rectum). 



Structure of the Large Intestine. 



We find here the same four coats which have been seen in the canal above : 

 serous, muscular, submucous, and mucous. 



The serous coat is the peritoneal covering investing parts of the large intes- 

 tine to a variable extent. 



The caecum is completely invested. The ascending and descending colons in 

 the adult have usually only a third of the posterior surface left bare. It is a 

 question when to declare the folds near enough to call them a mesocolon. 



Treves says a mesocolon may be expected on the left side in 36 per cent, of 

 all cases, on the right side in 26 per cent. 



The transverse colon is almost completely invested, having a proper meso- 

 colon ; the great omentum is attached to its anterior surface. 



The sigmoid flexure has a mesocolon, and the upper part of the rectum has a 

 mesorectum. In the second part of the rectum the peritoneum covers its ante- 

 rior surface and parts of the sides ; its third portion loses it altogether. The 

 peritoneum covering the internal taenia along the colon, especially the transverse 

 and after part, is thrown into many external pouches containing fat in well- 

 nourished people ; they are called appendices epiploicce, or omentula. 



The muscular coat consists of an external longitudinal and an internal circu- 

 lar layer. 



The longitudinal fibres are partly collected into three flat longitudinal bands, 

 each about half an inch wide and one twenty-fifth inch thick. They are found 

 on the caecum and colon and each is called ligamentum or tcenia coli Between 

 these bands the longitudinal layer is present, but very thin. On the appendix 

 the layer is uniform. These bands spread out from the root of the vermiform 

 appendix to the caecum. Thence they can be traced as far as the rectum, where 



they form two bundles. The posterior band passes 

 ^uca sijjmoidea along the mesenteric attachment of the intestine; 

 another, the largest, runs along the anterior border 

 of the ascending and descending colons and on the 

 transverse colon corresponds to the attachment of 

 the great omentum. The third or internal band 

 runs along the inner borders of the ascending and 

 descending colons, but becomes inferior on the trans- 

 verse colon. 



The three bands are about one-half shorter than 

 the real walls of the intestine and so form sacculi or 

 haustra (buckets). If the bands be dissected away 

 the sacculi will be wholly effaced and the colon be- 

 comes much elongated and cylindrical. The transverse constrictions seen on the 

 outside of the intestine between the sacculi appear on the inside as sharp ridges 



