684 THE NERVE-CELLS OF THE COED. [BOOK in. 



of posterior root, entering grey matter from external posterior column. 

 x. grey matter of posterior horn. Sp. a. bundles of fibres belonging to the 

 spinal accessory nerve ; in the lateral reticular formation they are seen cut 

 transversely, b. is a natural septum of connective tissue marking out the 

 cerebellar tract C. T. from the crossed pyramidal tract C. P. T. z. s. zona 

 spongiosa. 2 a, /3, 7, lateral cells of the anterior horn. 5. Cells in the region 

 of the lateral reticular formation. The other letters of reference are the 

 same as in Fig. 110. 



into connection with cells not far from the entrance of the root. 

 The cells with which the fibres are thus connected are situated 

 in various parts of the grey matter, on one or the other side of 

 the cord. Among these, we have reason to believe, are the cells 

 of the anterior horn giving off axis-cylinder processes to ante- 

 rior roots, and in this way a direct chain between afferent and 

 efferent fibres seems to be established. Others of these cells 

 give off axis-cylinder processes, which run upwards, headwards, 

 forming strands in the white matter of the cord and end in 

 parts, lying in many cases at least in the brain above the cord. 

 Such cells form relays in the transmission of afferent impulses; 

 the posterior vesicular cylinder, the column of Clarke, is a 

 group of such cells. 



In a certain number of cases however the (anterior divisions 

 of the) fibres do not make such speedy connections, but run 

 upwards in the median posterior column, column of Goll, which 

 indeed they for the most part form. Hence when a posterior 

 root is cut, degenerating fibres are found in the median poste- 

 rior column above the entrance of the root, and may be traced 

 as an 'ascending' degeneration right up to the spinal bulb. 

 The fibres coming from successive roots take up definite posi- 

 tions in the column as is illustrated in Fig. 114. The contri- 

 bution to the column furnished by each root diminishes however 

 upwards, as shewn by the diminishing area of degeneration; 

 that is to say, some of the fibres of the posterior root after 

 running in the median posterior column for a greater or less 

 distance, and the distance may be considerable, eventually turn 

 aside, and enter the grey matter of the cord; here they end in 

 connection with nerve cells. The contribution to the column, 

 though thus diminished, may be traced to the spinal bulb; here 

 the remaining fibres of the root end in connection with the cells 

 of the gracile nucleus. 



Thus the fibres forming the posterior root of each spinal 

 nerve have a wide and manifold grip upon the central nervous 

 system. Some stretch right beyond the spinal cord and lay 

 hold of the spinal bulb ; and these, it will be remarked, keep 

 entirely to the side on which they enter. Others, running for 

 variable distance in the posterior median column of the same 

 side, lay hold of the grey matter, it may be far above the 

 entrance of the root, while yet others lay hold of the grey mat- 

 ter soon after their entrance into the cord, and that either above 



