THE DIGESTIVE TRACT. 



173 



lymphoid cells are everywhere so closely packed that the support- 

 ing reticulum of connective tissue is masked. In the upper part of 

 the duodenum numerous ill-defined masses of adenoid tissue occupy 

 the mucosa between the follicles and represent the lenticular glands 

 of the stomach. 



The agminated glands^ or Payer's patches, are large, oval 

 groups of closely aggregated lymph-follicles, held and blended to- 

 gether by diffuse adenoid tissue. These patches vary in size and 

 number, and are usually limited to the lower two-thirds of the small 

 intestine, reaching their highest development in the ileum, where 

 they may attain a length of 9-1 1 cm. ; between twenty and thirty 

 patches generally are present, while they are relatively better devel- 

 oped in young than in old subjects. 



The agminated glands appear first within the mucosa, but later 

 encroach largely upon the submucous tissue. The lymph-follicles 

 of which these patches are composed become somewhat pyramidal, 

 owing to pressure, and lose much of their individuality, the demarca- 

 tion into separate follicles being best preserved along the outer 



FIG. 214. 



Section of small intestine of child, including a portion of a Peyer's patch : a, b, and c , mucosa, sub- 

 mucosa, and muscular coats ; d, villi ; e, e, atrophic follicles of the mucosa. 



boundary, occupying the submucosa, within the mucosa the out- 

 lines of the follicles being lost in the general adenoid mass. Where 

 the summits of the follicles impinge against the inner layer of the 

 mucosa, the positions of the follicles are indicated by corresponding 

 elevations of the mucous surface, at which points the villi are fre- 

 quently pushed aside and the gland-layer more or less completely 

 interrupted. In the vermiform appendix of some animals, and 



