CH. Vll.j 



DEVELOPMENT OF NKRVE FIBRES 



79 



end-plates occurs in different parts of the animal kingdom. Some- 

 what similar nerve-endings are seen in tendon ; these, however, are 

 doubtless sensory (figs. 98, 99). 



In the involuntary muscles, the fibres, which are for the most part 

 non-medullated, form complicated plexuses near their termination. 

 The plexus of Auerbach (fig. 100) between the muscular coats of the 

 intestine is a typical case. Groups of nerve-cells will be noticed at 

 the junctions of the fine nervous cords. From these plexuses fine 

 branches pass off and bifurcate at frequent intervals, until at last 

 ultimate fibrillse are reached. These subdivisions of the axis cylinders 

 do not anastomose with one another, but they come into close relation- 



FIG. 100. Plexus of Auerbach, between the two layers of the muscular coat of the intestine. (Cadiat.) 



ship with the involuntary muscular fibres ; though some histologists 

 have stated that they end in the nuclei of the muscular fibres, it is 

 now believed that they do not pass into their interior. 



The terminations of sensory nerves are in some cases plexuses, 

 in others special end-organs. We shall deal with these in our study 

 of sensation. 



Development of Nerve-fibres. 



A nerve-fibre is primarily an outgrowth from a nerve-cell, as is 

 shown in the accompanying diagram (fig. 101). A nerve-cell, though 

 it may have many branches, only gives off one process which becomes 

 the axis cylinder of a nerve-fibre. This acquires a medullary sheath 



