ISO ELEMENTAET PBTSIOLOGT. [XVII. 



a. Tlie epithelium lining them consists of 

 short columnar cells. Observe their 

 gradation into the cells covering the 

 villi; usually they have a clear free 

 border like that of the columnar cells 

 of the villi. 



jS. There is usually a distinct basement 

 membrane immediately beneath the epi- 

 thelium. This is formed of connective- 

 tissue corpuscles very much flattened 

 and fused together into a membranous 

 sac; the outliaes of the cells are not 

 seen in the section, but the nuclei are 

 fairly conspicuous. 



7. The lumina of the glands are in thin 

 sections distinct. 



c. The adenoid tissue around the bases of the 

 glands of Lieberkiihn and between them and 

 the muscularis mucosae. This, unlike the 

 corresponding tissue in the stomach (Lesson 

 XVI. A, § 2, c), has a large number of leuco- 

 cytes in its meshes. 



d. The lymph follicles ; either isolated, or ag- 

 gregated ipto Peyer's patches ; the follicles 

 are round or oval masses of adenoid tissue 

 crowded with leucocytes, lyiag immediately 

 beneath the surface epithelium and usually 

 stretching down into the submucous tissue. 

 They are in the midst of the glands of Lie- 

 berkiihn, and the villi are absent over them. 



