302 



THE DIGESTIVE SYSTEM 



The ileo-caecal valve, which guards the orifice hy which the 

 small intestine opens into the caecum, is formed by a reduplication 

 of the mucous membrane, which is strengthened by a thickening 

 and overlapping of the circular muscular layers of both small and 

 large intestines. 



The outer longitudinal muscular layer is continued directly 

 from the wall of the ileum to that of the caecum, and therefore 



FIG. 246. TRANSECTION OF THE VERMIFORM APPENDIX OF MAN. 



The submucosa contains much adipose tissue, and a number of large lymphoid nodules, 

 each with a dense periphery and a large, lighter, germinal center. Photo, x 10. 



pursues a relatively shorter course than either the internal muscu- 

 lar layer or the mucous membrane. Section of only the outer layer 

 of the muscular coat permits one to straighten the fold of the 

 intestinal wall and thus obliterate the valve. In other words the 

 outer muscular layer is not included in the valvular reduplication. 

 The muscularis mucosae is slightly thickened at the margin of 

 the valve. At this point, also, the villi become shorter and at the 

 margin of the caecal surface of the valve they entirely disappear. 



The following tabulated statement of the more important 

 characteristics of the several portions of the alimentary tract may 

 be of assistance to the student in the differential diagnosis of these 

 organs. 



