!68 NORMAL HISTOLOGY 



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and to the gastric glands; the exact mode of termination of these 

 nerve-fibrillae within the mucosa, however, is still undetermined. 



THE INTESTINES. 



The four coats of the stomach are continued, with little modifica- 

 tion, into the mucous, the submucous, the muscular, and the 

 serous tunics of the intestinal wall ; the variations characterizing 

 the several divisions of this tube are dependent largely upon modi- 

 fications and specialisations of the mucous membrane. 



The free inner surface of the small intestine is studded over with 

 small cylindrical elevations the villi projecting into the intestinal 



lumen and bathed in the 



_ FlG - 2 5- juices of the canal. In 



addition to the villi, which 

 are found through the 

 whole extent of the small 

 intestine, the mucous 

 membrane is thrown into 

 transverse or oblique per- 

 manent folds the val- 

 vulae conniventes 

 which extend partially 

 around the tube, and are 

 most marked in the duo- 

 denum and the jejunum ; 

 these folds increase the 

 area of the mucous sur- 

 face, and are beset with 

 villi the same as the sur- 

 rounding parts of the 

 mucosa. These projections, the villi and the valvulae conniventes, 

 are peculiar to the small intestine and serve to distinguish it from 

 the large. 



The mucosa is covered by a single layer of columnar epithelium 

 resting upon the basement-membrane. The prismatic cells contain 

 finely granular protoplasm and oval nuclei, the latter being usually 

 situated within the inner half of the cell. The outer free ends of 

 the cells are invested by a peculiar cuticular zone, or basilar border, 

 a well-defined continuous band exhibiting, in suitably preserved 

 specimens, a fine vertical striation. The significance of these mark- 

 ings is still uncertain, especially in view of the fact that, after the 

 action of such reagents as water, the border breaks up into rods 

 resembling very coarse cilia ; the striation is regarded by others as 

 the expression of fine parallel canals. 



Longitudinal section of human small intestine, showing 

 general relation of the folds constituting the valvulae conni- 

 ventes to the mucosa and submucous coat; the latter con- 

 tributes the fibrous core over which the mucosa with its villi 

 and glands extends. 



