SMALL INTESTINE 



265 



the cells, forming a reticular mass between them and the tunica propria (C). After 

 the spherules had broken down and had probably been transferred to the blood vessels, 

 the tunica propria entered into its usual relation with the shortened epithelium (D). 

 The basal protoplasm was then restored. According to this interpretation protein 

 absorption is accomplished as a secretory process of the epithelium, the product being 

 eliminated from its basal portion. The spherules accumulate at and near the tips of 

 the villi, in spaces which many authorities describe as due to the artificial retraction 

 of the tunica propria (Fig. 260, a). The spherules have been considered a coagulum 

 of the fluid squeezed from the reticular tissue. In part they may be boundaries of 

 the basal ends of epithelial cells on the distal wall of the villus. 



Sections of villi. 



Ephitelium 



Muscularis 

 macosae. 



Submucosa. Intestinal glands. Oblique sections of intestinal glands. 



FIG. 260. VERTICAL SECTION OF THE Mucous MEMBRANE OF THE JEJUNUM OF AN ADULT MAN. X 80, 

 The space, a, between the tunica propria and the epithelium of the villus is perhaps the result of the shrink. 



ing action of the fixing fluid. At b the epithelium has been artificially ruptured. The goblet cells 



have been drawn on one side of the villus on the right. 



Outer layers of the small intestine. The tunica propria, which forms the 

 cores of the villi and extends between the glands, is a reticular tissue, 

 containing the usual types of free cells and also a large number of plasma 

 cells (see p. 68). Slender strands of smooth muscle extend up and down 

 the villi, being inserted into the reticulum, and by contraction they cause 

 the villi to shorten. The muscularis mucosa consists of an inner circular 

 and an outer longitudinal layer, thus duplicating on a small scale the tunica 

 muscularis. The submucosa is a connective tissue layer, such as has been 

 described in the stomach and oesophagus, and the muscularis is divided into 

 a thick inner circular layer of smooth muscle and a thinner outer longitu- 

 dinal layer, between which is a thin stratum of intermuscular connective 



