COURSE OF THE FIBRES IN THE SPINAL CORD. 363 



ther forwards, are imbedded in the middle of the grey substance. 

 The nerve cells of the posterior cornua are amongst the smallest, 

 and are not, like those of the anterior cornua, collected into 

 groups, but are distributed through that part of the posterior 

 cornua which, like the anterior, is traversed by a fine plexus of 

 nerve fibres. 



COURSE OF THE FIBRES IN THE SPINAL CORD. 



The methods of research with which we are at present 

 acquainted are scarcely adequate to enable a precise and 

 detailed description of the course of all the fibres in the spinal 

 cord, which necessarily constitutes the foundation of the 

 physiology of the organ, to be given. Nevertheless, the ob- 

 servations that have been already made at least permit us to 

 draw a sketch with a tolerably firm hand of the direction pur- 

 sued by the nerve fibres entering the anterior roots of the 

 nerves, though our knowledge of the course of those forming 

 the posterior roots is still very defective. 



The fibres of the anterior roots on entering the cord traverse 

 the white substance obliquely, without otherwise contributing 

 to form it, and pass directly to the grey substance of the 

 anterior cornua with the processes of the nerve cells of which 

 they are immediately continuous ; these cells are consequently 

 to be regarded as the origins of the fibres of the anterior roots. 

 The protoplasmic processes of these cells form parts of the fine 

 nerve-fibre plexus of the grey substance, from which larger- 

 fibres proceed, which, running in opposite directions, leave the 

 grey substance, and ascend to the brain in the white columns. In 

 consequence of this constant accession of nerve fibres to the 

 white substance, it must necessarily augment in bulk from 

 below upwards. In regard to the course of the nerve fibres 

 emerging from the grey substance of the anterior cornua, two 

 sets, a median and a lateral, must be distinguished. The median 

 enter immediately into the anterior white commissure, where 

 they decussate with the corresponding fibres of the opposite 

 side, and at a higher point enter the anterior column of the 

 opposite half of the cord. The lateral fibres attach themselves 

 to the lateral columns of their own side, in which they ascend 



