CHAP. XI.] OFFICE OF THE POSTERIOR COLUMNS. 319 



anterior or posterior columns were irritated,* much stronger mo- 

 tions being excited by the posterior than by the anterior columns. 



It is clear, then, that we must not draw any other conclusion from 

 experiment than that the antero-lateral columns appear to be motor 

 in their function. Respecting their sensitive power we gain no infor- 

 mation from this source; and it must be confessed that our knowledge 

 is no more advanced by it as regards the posterior columns. 



We are much disposed to think that the antero-lateral columns 

 are the centres of the main actions of the cord, whether mental or 

 physical. Both roots of the nerves are connected with these 

 columns, and therefore fibres of sensation and of motion must be 

 found in them. These columns are always proportionate to the 

 nerves which arise from them. : they enlarge when the nerves are 

 large, and contract when the nerves diminish in size. The poste- 

 rior columns, on the other hand, are of uniform dimension 

 throughout nearly the entire length of the cord, although the pos- 

 terior roots of the nerves exhibit considerable difference in point 

 of size in different regions. 



We venture to suggest that the posterior columns may have a 

 function different from any hitherto assigned to them. They may 

 be in part commissural between the various segments of the cord, 

 and in part subservient to the function of the cerebellum in 

 regulating and co-ordinating the movements necessary for perfect 

 locomotion. 



The analogy of the brain, in which the various segments are 

 connected by longitudinal commissures, suggests the probable ex- 

 istence of fibres similar in office for the spinal cord. If we admit 

 such fibres to be necessary to ensure harmony of action between the 

 several segments of the encephalon, there are as good grounds for 

 supposing their existence in the cord, which in reality may be 

 regarded as consisting of a number of ganglia, each a centre of 

 innervation to its proper segment of the body, and therefore 

 requiring some special connecting fibres to secure consentaneous 

 action with the rest. 



The attribute of locomotive power rests upon the connexion of 

 the posterior columns with the cerebellum, and the probable in- 

 fluence of that organ over locomotion. If the cerebellum be the 

 regulator of locomotive actions, it seems reasonable to suppose that 

 those columns of the cord which mainly pass into it, should enjoy a 

 similar function ; that, as they are the principal medium through 

 which the cerebellum is brought into connexion with the cord, it 

 * See his translation of Muller's Physiology, Second Edit., p. 796*. 



