MODE OF ORIGIN OF NERVE FIBRES IN NERVE CENTRES. 185 



as composed essentially of only a nucleated enlargement of the axis 

 cylinder. If we pass to a more central portion of the nervous system, 

 we meet with the multipolar ganglion cells of the spinal cord, or of 

 the medulla oblongata, from which, according to the important dis- 

 covery of Deiters, the axis cylinder of the fibre in question proceeds 

 as an undivided process. The numerous other processes of the 

 cell connect it, and by its means the axis cylinder, with more 

 distant regions of the central organs, and probably also of the peri- 

 phery of the body, but clearly do not entitle us to regard the 

 ganglion cell as the exclusive origin of the nerve fibre. If we compare 

 the axis-cylinder process with the stem of a plant and its divisions, 

 and the peripheric terminal organs with the branches, leaves, and 

 flowers, the ganglion cell is equivalent to the root stock, and the 

 branched processes to the subterranean root fibres. It is requisite to 

 follow these out in order to arrive at the extremity opposite to the 

 peripheric termination. In consequence of the evidence I have 

 adduced of the exquisitely delicate fibrillar structure of the ganglion 

 cell substance, and of all its processes, a path is opened by which we 

 may investigate the true central terminations of the fibrils entering 

 into the composition of the axis cylinder. Unfortunately, the indi- 

 vidual fibrils within the substance of the cells escape all accurate 

 observation. 



The above comparison of the ganglion cells and their processes 

 with the root stock, stem, and root fibres of a plant, is, after all, like 

 most comparisons, only an imperfect one. The branched processes of 

 a multipolar ganglion cell, such, for instance, as may be found in the 

 anterior horn of the spinal cord, have certainly not all been satisfactorily 

 ascertained to pass as primitive fibrils to the axis-cylinder process ; 

 but rather this receives only a single group, the remainder extending 

 as branched processes in other directions. Thus the ganglion cell con- 

 stitutes a common point of union of numerous separate fibrils proceed- 

 ing from widely different regions of the nervous system ; and whilst 

 one of these associated bundles becomes the axis cylinder of a fibre, 

 and after becoming invested by a medullary sheath, immediately runs 

 peripherically, the others pass in unknown directions. 



It remains to consider whether, admitting that a large number of 

 the fibrils are already formed, and only traverse the ganglion cells, 

 there may not be some which do actually originate in these. In regard 

 to this point, the interfibrillar granular substance is first to be noticed, 

 which is probably a residue of the embryonia protoplasm, by the 

 agency of which the fibrils are differentiated ; a substance which pos- 

 sibly remains in greater abundance in the immediate vicinity of the 



