122 



NORMAL HISTOLOGY. 



supplied. When near the mucous membrane, they occupy the microscopic 

 ganglia within the submucous layer. Surfaces highly endowed with sensi- 

 bility are generously provided with twigs containing medullated fibres. 

 As the latter approach their destination, they lose their medullated char- 

 acter and, as naked axis-cylinders, form subepithelial plexuses from which 

 fibrils pass into the papillae, where some terminate in free or special end- 

 ings. Others enter the epithelium and penetrate between the cells for 

 a variable distance to end free, for the most part, in minute bulbous 

 swellings. 



Non-vascular epithelium 

 Terminal capillary loops 



.Tunica propria 



Larger branches within 

 submucosa 



FIG. 161. Section of injected oral mucous membrane ; the terminal capillary loops occupy the papillae of 



the tunica propria. X 60. 



THE GLANDS. 



Glands are essentially outgrowths from the epithelium of mucous 

 membranes, the epithelial elements becoming modified into gland-cells 

 which assume the role of secretion-forming organs, whose products are 

 discharged on the free surface and keep the latter moist. This last pur- 

 pose, however, is incidental in the case of many important glands, as the 

 parotid, pancreas or liver, since these organs supply secretions for partic- 

 ular ends. 



The simplest type is the unicellular gland found in the lower forms; in 

 principle this is represented in man and the higher animals by the goblet- 

 cells which occur in profusion in mucous membranes covered with columnar 

 epithelium. The viscid secretion, or mucus, poured out by the goblet-cells 

 serves to protect and lubricate the surface of the mucous membranes. The 

 term "gland," however, commonly implies a more complex organ, com- 

 posed of an aggregation of secretion-producing cells enclosed within connec- 



