THE DIGESTIVE SYSTEM 271 



that of the large intestine. The glands vary in number, but are usu- 

 ally much less closely packed than in the large intestine. They are 

 most numerous in the appendices of infants and children. The 

 glajid tubules (Fig. 174, j) are usually rudimentary, but in most cases 

 have the same structure as the intestinal glands, and are evidently 

 functional as they contain mucous cells in all stages of secretion. In 

 consequence of the wider separation of the tubules the stroma is more 

 abundant than in the large intestine, but has the same structure. 

 The miiscularis mucosce is usually fairly distinct as a thin circularly 

 disposed band of smooth muscle cells just beneath the stroma. It is 

 not always present. In some cases the mucosa as such is practically 

 absent, being replaced by fibrous tissue. This condition is especially 

 common after middle age, and may or may not be associated with 

 obHteration of the lumen. 



2. The submucosa (Fig. 174, e) is similar to that of the intestine. 



3. The muscular coat varies greatly, both as to thickness and 

 as to the amount of admixture of fibrous tissue. The inneru;ircular 

 layer (Fig. 174, d) is usually thick and well developed.- The outer 

 longitudinal layer (Fig. 174, c) differs from that of the large intestine 

 in having no arrangement into lineas, the muscle tissue forming a con- 

 tinuous layer. Less commonly a more or less marked tendency to an 

 arrangement of the cells of the longitudinal coat into bundles, be- 

 tween which the outer coat is thin or wanting, is observed. 



4. The serosa has the usual structure of peritoneum. 



The lymph nodules (Fig. 174, h) constitute the most conspicuous 

 feature of the appendix. They He mainly in the submucosa. In 

 children and young adults the nodules are oval or spherical; in later 

 Ufe somewhat flattened. The nodules may be entirely distinct, or 

 may be arranged as in a Peyer's patch with distinct apices and bases, 

 but with their central portions confluent. The muscularis mucosae 

 either passes through the superficial portions of the nodules, or, where 

 they are separated from the lumen, passes over them. 



The distribution of blood-vessels, lymphatics, and nerves is 

 similar to that in the large intestine. 



The Rectum 



I. The mucous membrane of the rectum has a structure similar 

 to that of the large intestine (Fig. 175). The glands are longer and 

 the mucosa is consequently somewhat thicker. In the lower part of 

 the rectum definite longitudinal foldings of the mucosa occur, the 



