NERVES OF THE SMALL INTESTINE. 



215 



Nerves. The small intestine is supplied by branches of the superior 

 mesenteric plexus of the sympathetic system. This plexus is ventral to 

 the aorta, and sends branches through the mesentery into the serosa. 

 The manner in which they penetrate the other layers, forming the myen- 

 teric plexus [Auerbach's plexus] in the intermuscular connective tissue, and 

 the submucous plexus [Meissner's plexus] in the submucosa is shown in 

 Fig. 239, C. In surface view, obtained by stripping the layers apart, 

 these plexuses are seen in Fig. 242. Their branches supply the smooth 

 muscle fibers. From the submucous plexus the nerves extend into the villi, 

 where nerve cells have been detected by the Golgi method (Fig. 239, C); 

 it has been suspected, however, that some of these 'nerve cells' are portions 

 of the reticular tissue. Their terminations require further investigation. 

 Most of the intestinal nerves are nonmedullated but they include a few 

 large medullated fibers said to have free endings in the epithelium. 



FIG. 243. TRANSVERSE SECTION OF THE HUMAN VERMIFORM PROCESS. X 20. (Sobotta.) 

 Note the absence of villi and the abundance of nodules. Clear spaces in the submucosa are fat cells. 

 Only a part of the circular layer of the muscularis has been drawn. 



LARGE INTESTINE VERMIFORM PROCESS. 



The entire large intestine is characterized by the presence ol intestinal 

 glands associated with the absence of villi. In human embryos of from 



