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MANUAL OF PHYSIOLOGY. 



points. One of these, a closely meshed plexus with flattened 

 cords and ganglionic masses at their points of union, lies between 

 the longitudinal and circular layers of muscle (Figs. 56, 57) 

 forming the plexus myentericus exterior of Auerbach, and most 

 likely has to do with the movements of these layers of muscle. 

 The other lies internal to the circular muscle, in close relation to 

 the muscularis mucosse, and is called the plexus myentericus in- 



FIG. 56. 



FIG. 57. 



FIG. 56. Auerbach's plexus from between the muscle coats of the in- 

 testine, with low power. 



FIG. 57. A nodal point of Auerbach's plexus under high power, show- 

 ing the nerve cells. 



terior of Meissner ; the meshes of which are looser and more 

 irregular, and the cords and ganglia more rounded and finer than 

 those of Auerbach's plexus. (Figs. 58, 59.) 



The blood flowing through these nerve centres in all probability 

 acts as a sufficient stimulus under ordinary circumstances, to pro-< 

 duce some peristaltic motions, and hence we may say that they 

 are automatic. When food comes into the intestine it increases 

 the flow of blood, as well as mechanically irritating the intestinal 

 wall. The intestinal vessels remain engorged so long as the pro- 

 cess of digestion goes on. Food seems to act more effectually 

 than insoluble mechanical stimuli, for when insoluble substances 

 are placed in the gut, they at first call forth active movements; 

 but these do not last long, for the stimulus is not of itself ade- 



