898 THE NATURE OF THE GREY MATTER. [BOOK in. 



section shews numerous distinct nerve fibres crossing it in various 

 directions ; of these fibres a few are ordinary medullated fibres, 

 some are non-medullated fibres, that is to say, are naked axis- 

 cylinders, while others, and these the more numerous, are the 

 peculiar medullated fibres of small diameter spoken of in 563. 

 A large number of these fibres, indeed all the larger ones, though 

 they go to make up what we call grey matter, are not continuous 

 with, and do not belong to, the groundwork or nervous web, at all 

 events, do not form part of the groundwork seen in the same 

 section as themselves. They are simply fibres traversing the 

 groundwork, in spaces of the neuroglia bed, on their way up or 

 down the cord or across the cord from one part to another. It 

 may be that some of the finer medullated fibres do really enter 

 into the groundwork, and so contribute to the nervous web ; but 

 our knowledge is too imperfect to afford a clear decision on this 

 point. Our inability to define its exact limits need not, however, 

 prevent our recognising the existence of the groundwork. 



The prominence in this groundwork of the larger nerve-cells 

 has led to the conception that the powers of the spinal segment 

 are exercised by these nerve-cells to the exclusion of the other 

 elements of the nervous web. But such a view has not been 

 adequately proved. What we do know is that the nuclei and 

 cell-bodies of the cells of the anterior horn exercise an important 

 influence on the nutrition of the fibres of the anterior root which 

 proceed from them, and possibly also influence the nutrition of the 

 other branches of the cells forming part of the groundwork ; and 

 these cells are probably so conspicuous a feature of every section 

 of the spinal cord because of the important task entrusted to them 

 of maintaining in due order the nutrition of the long stretch of 

 motor fibres reaching from them to the muscular fibres or other 

 peripheral organs. The fibres of the posterior root are not so 

 obviously connected with the conspicuous cells of the grey 

 matter; indeed as we have said it may be doubted, though the 

 view is maintained by some, whether any cell intervenes to secure 

 the continuity of a posterior fibre with the groundwork, a division 

 of the axis-cylinder serving this purpose ; and this becomes 

 intelligible when we bear in mind that the posterior fibres are 

 governed as far as their nutrition is concerned by the nerve-cells 

 of the ganglion on the posterior root, which ought probably to be 

 considered as much a part of the spinal cord as the cells of the 

 anterior horn. The nerve-cell of the ganglion is adequate to 

 secure the due nutrition of the nerve fibre until it joins the 

 groundwork, and probably helps to maintain the nutrition of the 

 groundwork itself. 



Hence we may perhaps, until fresh evidence to the contrary is 

 brought forward, incline to the view that the powers of the grey 

 matter do not depend on the conspicuous cells alone or even 

 chiefly, but on the peculiar molecular constitution and nature of 



