MINUTE STRUCTURE. 501 



Origin of the spinal nerves. — The anterior and posterior roots of 

 the spinal nerves are attached along the sides of the cord, and oppo- 

 site to the corresponding cornua of the grey matter ; the posterior 

 roots in a straight line at the posterior lateral gi'oove, and the anterior 

 roots scattered somewhat irregularly upon the surface (fig. 3i7, b). 



The fibres of the anterior roots may be traced into and through 

 the anterior cornua (fig. 350, e, e). In it they diverge in different 

 directions, passing among tlie large multipolar cells with which some 

 are probably connected. Many fibres pass backwards in the substance 

 of the anterior cornu, where some of them would appear to form 

 connections with fibres proceeding from other parts of the cord, and 

 others to spread obliquely upwards and downwards ; an external group 

 reach the lateral column, and an internal group cross in the anterior 

 white commissure to the anterior cornu of the opposite side. 



The fibres of the posterior roots, on reaching the posterior cornu, 

 diverge from each other and enter the grey substance, some immediately 

 through the substantia gelatinosa, others after curving through the 

 outer portions of the posterior columns and round the inner side of the 

 caput cornu (fig. 350, 9). Of those which pass through the gelatinous 

 substance, a large number immediately turn upwards and downwards, 

 and blend with the fine plexus of nerve-fibres which constitutes the 

 central portion of the grey matter, reaching, probably, some the anterior 

 cornu, and others by the posterior commissure the opposite side of the 

 cord. Of the fibres of the posterior roots which enter the grey 

 substance in front of the substantia gelatinosa, some pass forwards at 

 once through the grey substance, while others enter and blend with 

 the posterior vesicular columns of nerve-cells. Another set of fibres 

 slant principally upwards, but some downwards, in the white substance 

 of the posterior columns, and, interlacing with each other, most pro- 

 bably enter the grey matter at different heights. Some are lost to view 

 in the posterior white columns, and it is uncertain whether or not 

 they immediately ascend through these columns to the brain. 



A narrow grey line extends from the apex of the posterior horn to the 

 posterior lateral furrow, and consists of connective tissue and fine nerve 

 fibres. It was formerly thought to be part of the posterior nerve root. 



Much discussion has taken place as to the coiu-se of the fibres in the cord, and 

 their ultimate destination. It is easily understood that, by the examination of 

 sections difficult to prepare, limited in extent, liable to undergo changes in the 

 preparation, and giving views confined each to little more than a thin lamina, 

 it is scarcely to be expected that the full history of many tortuous fibres can be 

 accm-ately ascertained. Thus it remains still undecided whether any of the 

 fibres of the nei-ve-roots pass up all the way to the brain. Volkmann concluded 

 that none of them reached the brain, arguing from measurements of the size of 

 the cord in different regions, that the cord could not contain in its upper regions 

 all those nerve-fibres which were traceable to it in the lower. Kolliker pointed 

 out the fallacy of this conclusion, in so far as Volkmann had not made proper 

 allowance for the diminished size of the fibres as they ascend in the cord ; but 

 although Volkmann's argument was thereby invalidated, it appears impossible 

 to prove by microscopic observations that fibres of nerve-roots traced into the 

 grey matter, and observed to emerge into the white matter, do not again re-enter 

 the grey and terminate there. 



There seems little doubt that the radiating prolongations of the cells are in 

 actual continuity with the axial filaments of nerve-fibres, whether proceeding- 

 from nerve-roots or from different parts of the cord itself. 



