272 



HISTOLOGY 



dition is found in scarcely 50% of individuals over forty years of age 

 (Stohr). Often the lumen is narrowed or even obliterated. The epithe- 

 lium with its glands and the lymphoid nodules then disappear, and are 

 replaced by an axial mass of fibrous tissue. This is surrounded by the 

 unaltered submucosa and muscularis; the serosa may show the results of 

 inflammatory conditions. 



CAECUM AND COLON. 



The human caecum and colon contain villi only in the embryo. These 

 villi disappear at about the sixth month. The production of new cells 

 does not keep pace with the expansion of the epithelial tube, and the villi 



Glands. 



Epithe- 

 lium. 



Submu- 

 cosa. 



Fat cells. 



Solitary nodule with germinal center. 



FIG. 268. VERTICAL SECTION OF THE Mucous MEMBRANE OF THE DESCENDING COLON OF AN ADULT 



MAN. X 80. 



The fat has been blackened with osmic acid. Compare the length of the glands with those of the small 

 intestine (Fig. 260), from the same individual and drawn under the same magnification. 



therefore gradually flatten and disappear. In the parts of the embryonic 

 intestine distended with secretions and desquamated cells (constituting 

 the meconium), the villi disappear earlier than in the contracted portions 

 (Johnson) . 



After the villi have gone, the mucosa contains only tubular pits or 

 glands, lined with simple columnar epithelium (Fig. 268). These glands 

 are similar to those in the small intestine but are longer sometimes 

 twice ^as long (0.4-0.6 mm.). They contain more goblet cells, but cells 



