88 PRACTICAL MICROSCOPY. 



(H.) 



2. The epithelium of gland-tubes. (The upper portion of the 

 tubes will be cut obliquely in many places, as they may have been 

 inclined, and the epithelium will show as a beautiful mosaic of poly- 

 gonal areas.) (a) The differentiation between border and central 

 cells, (b) Tubes cut transversely, showing the lumina. (c) Indi- 

 cations of the capillary plexuses between the tubes. 



3. The mucosa. (a) Arterioles and venules beneath the tu- 

 bules, (b) Scattered lymphoid cells (round cells with one, two, or 

 three nuclei). 



4. The muscularis mucosae. (Note the elongated nuclei of the 

 smooth muscle cells.) 



5. The submucosa. (a) Arteries, veins, etc., cut in various 

 directions, (b) The adipose tissue. (Crystals of the fatty acids 

 are frequently seen in the cells when freshly mounted.) 



6. The muscular bundles of the circular layer with the septa of 

 connective tissue. (Note particularly the various appearances pre- 

 sented by bundles of involuntary muscular fibre when cut in different 

 planes.) 



SMALL INTESTINE. 



The histology of the intestine, both large and small, is formed upon 

 the general plan of that of the stomach. The same layers are pre- 

 sented: the mucosa, with its epithelial covering; the muscularis 

 mucosce; the submucosa; the muscular and the peritoneal coats. 



The mucosa of the small intestine is everywhere pierced by blind 

 depressions; or, what is equivalent, the surface is studded with 

 minute elevations or papillae, between which are the depressions which 

 correspond to the tubules of the stomach. The elevations are called 

 villi 9 the depressions between the villi, crypts. 



The small intestine serves two important functions: 1, The secre- 

 tion of a fluid, one of the digestive juices the succus entericus. 2, 

 The absorption of food, especially the fats or hydrocarbons. 



We shall view the histology of this organ from a physiological 

 standpoint, considering: 1st, Those structures concerned in the secre- 

 tion of the succus entericus; 2d, Those portions concerned in absorp- 

 tion of food. 



HISTOLOGY OF THOSE PARTS OF THE SMALL INTESTINE PARTICU- 

 LARLY CONCERNED IN THE PRODUCTION -OF THE SUCCUS 

 ENTERICUS. 



The diagram (Fig. 66) is intended to represent at A the thickness 

 of the mucosa with its papillary elevations the villi. The muscu- 



