1 68 



NORMAL HISTOLOGY. 



traversing the tunica propria, open directly on the free surface between 

 the crypts of Lieberkiihn. The columnar gland-cells lining the duodenal 

 alveoli are probably identical in nature with those of the pyloric glands. 



The crypts or glands of Lieberkiihn are simple tubular depressions 

 which are found not only throughout the small intestine, but the large one 

 as well. Under low magnification, the surface of the small intestine exhibits 

 numerous pits, the orifices of these crypts, which almost fill the spaces 

 between the bases of the villi; with the exception of the areas immediately 

 overlying the lymph-nodules, where they are displaced, these glands are 

 present in all parts of the intestinal tube. They are very closely set, narrow 

 and penetrate the tunica propria as far as the muscularis mucosee. In length 

 they vary from .2-. 4 mm., and in diameter from 60-80 //. The lining of the 

 crypts rests upon a delicate basement membrane and consists of a single 



Pyloric glands 



Circular mus 



cle sphincter 



pylori 



'^f'^ 



Longitudinal "ffipv'v,: 

 muscle a :-.'..'. 



Stomach 



Duodenum 



FIG. 209. Longitudinal section through junction of stomach and duodenum, showing transition of 

 pyloric into duodenal glands; also thickening of circular muscle to form sphincter pylori. X 15. 



layer of columnar cells, continuous with those covering the villi. They differ 

 from these in being shorter and without the cuticular border seen on the 

 villi. In view of the presence of mitotic figures within the crypt-epithelium 

 of the adult, it is probable that the young cells here produced are gradually 

 pushed upwards and supply the elements required to replace the old worn- 

 out surface cells on the villi. Goblet-cells, as well as migratory colorless 

 blood-corpuscles, occur among the lining of the crypts. Constantly within 

 the human ileum, the deepest parts of the crypts of Lieberkiihn contain 

 small groups of granular elements, the cells of Paneth, whose significance 

 is undetermined. The duodenum, jejunum and vermiform appendix are 

 uncertain seats of these cells, while within the large intestine they are absent. 

 The fact that such cells are wanting in many orders of animals possessing 

 well developed intestinal crypts, points to some special, rather than a general, 

 purpose. 



Lymph-Nodules. The lymphoid tissue within the intestinal tube 

 occurs in the form of circumscribed nodules, which may remain isolated, as the 

 solitary nodules, or be collected into considerable masses, as Peyer" s patches. 



The solitary nodules vary greatly in number and size, sometimes 

 being abundant in all parts of the small intestine, at other times almost 

 wanting; usually they are few in the upper and numerous in the middle and 

 lower parts of the tube. They appear as small whitish elevations, spherical 

 or pyriform in shape and from . 2-2. 5 mm. in diameter. Villi and crypts of 

 Lieberkiihn are wanting over the prominence of the nodules (Fig. 210). 



