THE SPINAL CORD. 



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nothing is known, excepting that severance of a ganglion 

 from the nerve trunks to which it belongs, produces loss of 

 excitability and structural changes in afferent fibres of the 

 nerve. (Waller.) 



Functions of the white columns of the Spinal Cord. 



The most important anatomical facts relating to the channels by which 

 excitation is transmitted in the spinal cord, are (i) that the fibres of the 

 spinal nerves are not continued to the brain, but communicate with ganglionic 

 cells ; (2) that in the anterior roots this communication is direct, mediate in 

 the posterior, i.e. through the reticulum ; (3) that the anterior roots may be 

 traced through the anterior horns, to the anterior columns of the other side 

 by the white commissure, as well as to the anterior and lateral columns of the 

 same side ; (4) that the fibres of the posterior roots divide into two sets, of 

 which the smaller at once lose themselves in the substantia gelatinosa, the 

 larger division tending inwards towards the posterior columns, in which some 

 of the fibres appear to acquire a vertical direction ; (5) the sectional area of 

 the lateral columns of the spinal cord is, as measured at any part of its course, 

 proportional to the sum of the sectional areas of the nerves which enter it 

 below the section ; (6) the sectional area of the grey substance is proportional 

 to the sum of the sectional areas of the nerves which enter the cord in the 

 neighbourhood of the section. 



The most important results of experimental investigation 

 as to the channels of propagation in the cord may be stated 

 as follows : (i.) The fibres of the lateral columns are the 

 only channels of influence between the intra-cranial centres 

 and the lower limbs. (2.) The afferent fibres by which 

 excitation of either lower extremity influences the intra- 

 cranial centres, are contained in the lateral columns of the 

 opposite side. (3.) The fibres by which the intra-cranial 

 centres influence the muscles of either inferior extremity 

 are contained for the most part in the lateral column of 

 the same side. (4.) It is probable that the fibres of the 

 anterior and posterior columns serve as channels of com- 

 munication between neighbouring parts of the cord. 

 There is reason, however, for believing that in the lumbar 

 region, the posterior columns contain fibres by which 

 sensory impressions are transmitted upwards. 



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