

STRUCTUKE OF THE SMALL INTESTINE. 529 



their breadth is ? J 5 to 3^3 of an inch; and their aperture is g Jo to ?u 

 of an inch. They contain a simple conoidal epithelium, whose cells 



Fig. 357. Fig. 358 



(L 



Fig. 357. A. Transverse section of Lieberkiihn's tubes or follicles, showing the basement-mem- 

 brane and the sub-conoidal epithelium of their -walls, with the areolar tissue connecting the tubes : 

 a, basement-membrane and epithelium constituting the wall of the tube ; &, cavity or lumen of the 

 tube. (Magnified 200 diameters.) B. A single Lieberkiihn's tube, highly magnified ; an accidental 

 section in the oblique direction displays very distinctly the form and mode of packing of the epithe- 

 lial cells, the cavity of the tube, and the mosaic pavement of its exterior : a, basement-membrane ; 

 c, internal surface of the wall of the tube. (Magnified 200 diameters.) 



Fig. 358. Distribution of capillaries around follicles of mucous membrane. 



during digestion never contain fat, like those of the villi; the lumen 

 of the tube being filled by a clear fluid secretion the intestinal 

 fluid already described on page 201. The vessels of these glands 

 follow the type of those of the stomach. (Figs. 358, 355, and 353.) 



2. The racemose glands Brunner's glands most abundant in 

 the duodenum, resemble those of the oral cavity and the salivary 

 glands, in structure, and their vessels have the same arrangement 

 as those of the latter. (Fig. 348.) Thus the vessels whence the 

 secretion of these and the preceding glands is obtained are next to 

 the arteries, while those concerned in absorption (those of the villi) 

 are farther from them, and nearer to the veins. (Fig. 355.) 



3. The closed follicles are found scattered simply or in groups over 

 the walls of the small intestine. In groups, they constitute the 

 Peyer's patches, or glandulce agminatce. Each closed follicle is ??\ 2 

 to 2*4 or even T 1 2 of an inch in diameter, rounded or conical towards 

 the intestinal cavity, and lying partly in the corium of the mucous 

 membrane, and partly under it; extending from a point g o to 7 ^ 

 of an inch beneath its surface to the muscular tunic, which is here 

 more closely united with the corium. (Fig. 359.) On the surface 

 of the mucous membrane are roundish depressions, ^ to ^ f an 

 inch apart, corresponding to the separate follicles, and presenting 



34 



