INNERVATION OF THE DIGESTIVE TUBE 179 



directly into the muscle-layers where they terminate on smooth 

 muscle-fibers. Dendrites may also be traced from their cells of 

 origin into the commissures. Although in many instances it is 

 impossible to distinguish between axone and dendrites, there can 

 be no doubt that dendrites are present in the commissures. Not 

 infrequently several processes arising from the same cell may be 

 traced into a commissure leading from the ganglion in one direc- 

 tion while other processes arising from the same cell may be traced 

 into commissures leading from the ganglion in other directions. 

 In transverse or longitudinal sections axones as well as many of 

 the longer dendrites may be traced directly into the commissures 

 leading from the myenteric plexus into the submucous plexus. 

 In figure 2, A, which is taken from a longitudinal section of the 

 ileum of a kitten prepared by the methylene blue method, is 

 illustrated a commissure connecting a ganglion of the myenteric 

 plexus with a ganglion of the submucous plexus. This commis- 

 sure lies in the connective tissue between the muscle-bundles. 

 Individual nerve-fibers can not be traced from one ganglion into 

 the other in this section. However, nerve-fibers are present in 

 the commissure throughout its entire length. Figure 2, B, is 

 taken from a section through the posterior region of the oesopha- 

 gus of an embryo of the chick of ten days incubation prepared 

 by the pyridine-silver method. Neurones in the myenteric and 

 the submucous plexuses do not appear in these preparations. 

 Individual nerve-fibers uisiy, however, be traced from the myen- 

 teric plexus to the level of the submucous plexus. There can 

 be no doubt, therefore, that individual nerve-fibers extend from 

 one of these plexuses into the other. 



Suhviucous -plexus 



The ganglia of the submucous plexus, like those of the myenteric 

 plexus, are variously connected by commissures of non-medullated 

 fibers in which both axones and dendrites may be traced. These 

 commissures, in which the fibers are usually more or less com- 

 pactly aggregated, with the ganglia interposed at their nodal 

 points form a network which in general is confined to the sub- 



