40 THE STRUCTURE OF 



or accomplishments must correspond either with more 

 or less alteration of old, or with the development of 

 new structures, in one or more of the various nerve 

 centres. 



The Structural Relations of Nerve Cells with Nerve 

 Fibres, and with one another. 



Nerve cells are supposed to communicate with nerve 

 fibres and with one another in the following modes ; — 



1. The nerve cell occurs as a round or elongated swell- 

 ing in the course of a nerve fibre, as may he seen in figs. 

 10 and 11. 



Here an undivided nerve fibre sw^ells more or less abruptly 

 into the nerve cell, and similarly emerges therefrom, so 

 that the cell in this case is only a nucleated expansion of 

 the fibre. The fibrils of the axis band may be seen pass- 

 ing through the cell in a divergent and re-convergent 

 fashion, having the finely granular basis substance of the 

 cell between them. The sheath of the fibre, though 

 usually not the medullary substance (fig. 10), also passes 

 over the cell. 



A point which will be found more doubtful in other cases 

 is most distinctly illustrated here : viz., that a struc- 

 tural continuity exists between the substance of the cell 

 and that of the nerve fibre. There is no distinct line of 

 demarcation between the two. But, so far as we know at 

 present, this particular relation of fibre and eel] exists 

 principally in ganglia peculiar to the ingoing ner ves and 

 situated near the great centres to which these are attached. 

 There is, it is true, some reason for believing that a 

 similar relationship may exist in some of the ganglia on 



