338 ABDOMEN 



mucous membrane is pulled out from the interior of the muscular 

 tube it forms a tube about three times the length of the muscular 

 tube. It is not as a rule possible to pull out a portion of the mucous 

 tube from the interior of the muscular tube in formol-hardened 

 dissecting-room subjects, but the experiment is easily made in 

 the post-mortem room and the student should verify the above 

 statements at the first favourable opportunity. Finally, hold 

 the wall of the intestine to the light and note that whilst solitary 

 lymph nodules are present there are no aggregated lymph nodules. 



Structure of the Large Intestine. The walls of the large 

 intestine, like those of the small intestine, are formed by five 

 layers or coats of tissue: (i) Serous, (2) Subserous, (3) Mus- 

 cular, (4) Submucous, (5) Mucous. 



The Serous Coat is complete only in the cases of the caecum, 

 which is surrounded with peritoneum, and the vermiform 

 process, the transverse colon, and pelvic colon, which are 

 provided with mesenteries. The ascending colon, the descend- 

 ing colon, the iliac colon and the rectum have no serous 

 layer on their posterior aspects, and, in that respect, they 

 correspond with the second and third parts of the duodenum. 

 The anal canal is entirely devoid of serous covering. 



The special peculiarity of the serous covering of the large 

 intestine is the presence of numerous little fat-filled pouches 

 of the membrane, called appendices epiploicce, which project 

 from the free margin of the gut, and which are present on all 

 parts of the large intestine, except the vermiform process, the 

 lower part of the rectum, and the anal canal. 



The Subserous Coat is merely a thin stratum of areolar 

 tissue which connects the serous layer with the muscular 

 stratum. 



The Muscular Coat, as in the case of the small intestine, 

 consists of two strata, an external longitudinal stratum and 

 an internal circular stratum. 



The longitudinal stratum of muscle fibres forms a complete 

 covering only in the vermiform process, the rectum, and 

 the anal canal. In all other parts of the large intestine 

 it is arranged in the form of three longitudinal bands 

 whose positions have already been defined (see p. 337), 

 but may here be re-stated (i) One in relation to the 

 attached surface (t?enia mesocolica); (2) the second upon the 

 anterior aspect (taenia libera) ; (3) and the third along the 

 medial aspect of the gut, but, in the case of the transverse 

 colon, the latter band is in relation to the inferior aspect of 

 the tube (tsenia omentalis). The bands commence at the 



