394 OEIGINAL ARTICLES. 



substance, either to form loops, or to become continuous with the 

 fibres of the anterior roots, since the whole of the latter, as we shall 

 presently see, proceed directly to the grey substance. Indeed, (adds 

 Mr. Clarke), I have sometimes felt almost persuaded that a great 

 number of the fibres of these posterior roots are directly continuous, 

 in the grey substance, with those of the anterior roots ; but I caiuiot 

 make this statement with absolute certainty ; and as the question is 

 one of extreme difficulty, I shall hereafter endeavour to make it a 

 subject of special attention." 



The second kind of bundles which form the posterior roots tra- 

 verse the posterior columns transversely, and with different degrees 

 of obliquity from without inwards, extending nearly as far as the 

 posterior median fissure. They enter and pass through the grey 

 substance at various angles, and in compact bundles which decussate 

 and interlace each other in the most complicated manner. Some of 

 their fibres cross over to the opposite side through the posterior 

 commissure, behind the spinal canal ; others extend into the posterior 

 and lateral white columns ; and the rest may be traced deeply into 

 the anterior grey substance, where they separate in various directions 

 and are ultimately lost to view. 



The bimdles which compose the third kind of posterior roots 

 enter the cord obliquely. A few of their fibres proceed near the 

 surface both upwards and downwards, and pass out again with the 

 roots above and below them. The rest cross the posterior white 

 columns obliquely and chiefly upivards, a small number only passing 

 downwards. Interlacing with each other, and the other roots already 

 described, they diverge and reach the grey substance at points suc- 

 cessively more distant from their en trance in proportion to the obli- 

 quity of their course. The remainder, or most divergent, take a 

 longitudinal course with the fibres of the white columns, among 

 which tliey are lost. It is impossible to say whether any of these 

 longitudinal fibres are continued as far as the brain, or whether they 

 ultimately reach the grey substance of the cord. It is also extremely 

 difficult to trace the other fibres of these roots after they have reached 

 the grey substance. 



In the preceding account of the distribution of the posterior 

 nerve roots it will be seen that Mi'. Clarke anticipated the statements 

 of Brown-Sequard on the same point. (Grazette Medicale, 1855). 



Of the Anterior Roots, (fig. 6. a, a, a.) The anterior roots of the 

 spinal nerves, as Clarke formerly described them, traverse the anterior 

 part of the antero-lateral columns in distinct and nearly straight 

 bundles. They form no interlacement with each other, like the 

 posterior roots, until they reach the grey sulistance. Here their 

 fibres diverge in every direction, like the expanded hairs of a brush. 

 Some, near the margin, are easily seen to form loops with those of 

 contiguous buufUes ; others run outwards to the lateral columns, and 

 inwards to the antei-ior columns after decussating in the anterior 

 commissure with corresponding fibres from the opposite side. A 



