I04 THE SPINAL CORD AND CEREBELLUM 



fibres, which run longitudinally up the cord for some 

 distance between the posterior horn of gray matter 

 and the crossed pyramidal tract.* 



The distribution of the fibres of the posterior root is 

 complicated by the fact that on entering the cord they 

 are seen to divide, one portion running upwards and 

 one downwards, and, further, by the giving off of 

 collaterals or branches to other cells in the cord. 

 Some of the fibres, it will be seen — indeed, the great 

 majority — are coarse, whilst a smaller number are fine. 

 Most of the former travel upwards towards the spinal 

 bulb ; some, however, pass to Clarke's column, whilst 

 others either join the substantia gelatinosa of the 

 dorsal horn, or make connections with the motor cells 

 of the ventral horn, or, again, find their way to the 

 opposite side of the cord.t 



To thread the tangled maze of fibres thus arranged 

 is a very difficult task ; yet one thing seems tolerably 

 clear — the directions which they take indicate differ- 

 ences of function. If they do not tell us definitely 

 what the part of each set of fibres may be, yet they 

 furnish us with some data on which to base certain 

 conclusions. Knowing that the posterior root is the 

 sensory portion of each spinal nerve, and that the 

 cerebral cortex is the seat of perceived sensation, we 

 have reason to believe that those fibres which pass 

 upward towards the spinal bulb, and then by means of 

 certain relays — as to the nature of which some of the 

 highest authorities are not agreed — establish a con- 

 * Foster, he. cit., p. 949. t Ihid., p. 950. 



