of Movements in the Lumbar Region of the Spinal Cord. 247 



II. Minute Localisation within the Excitable Area. 



Repeatedly it -was found that with a minimal stimulus it was 

 possible to evoke movement either in the tail (and anns) only, or in 

 the hamstrings, or in the hip or in the side only, and whenever this 

 was obtained it was an invariable rule that the point for producing 

 movement in the tail was placed in the cord mesially of that point, 

 stimulation of which gave movement in the hamstrings, and that 

 this latter point was mesial of that for the hip, while most external 

 of all was the point from which movement of the side of the trunk 

 was elicited. This lateral arrangement has been in part foreshadowed 

 by the observations of Mott on the relation between the coccygeal 

 nerves and Goll's column. 



Investigation into the Segmental Representation of the Cord by Com- 

 parison of the Results of Excitation of the Anterior and Posterior 

 Roots. 



(a) Latency of Effect. Of course, in accordance with all previous 

 investigations, the delay in passing through the spinal cord was well 

 marked. 



(6) Character of Movement Elicited from the Respective Roots. 

 Stimulation of the peripheral end of an anterior root gave, on the 

 whole, a quick powerful extension of the whole limb, the latency, of 

 course, being extremely short ; on the other hand, excitation of the 

 corresponding posterior root resulted in a slower, though strong, 

 flexion of the whole limb with a well-marked latency. 



This remarkable functional distinction between the roots, viz., 

 anterior giving extension and posterior flexion, was quite constant, and 

 was obtained in every animal in which the experiment was made. 

 Of course, the movement which took place was a resultant effect, and 

 was produced by the contraction of many muscles, each muscle con- 

 tracting in whole, or in part, in combination with other muscles to 

 produce the extension or flexion respectively. 



The results with each root are given in the tables. 



Further, stimulation of a posterior root (say the 5th) produced 

 flexion of a joint or joints even when all the neighbouring anterior 

 roots but one were divided. Hence this flexion can only be due to 



I the stimulus passing from the posterior root through the spinal cord 

 along a particular anterior root to the muscles (differentiation of 

 function in the nerve centre of that root), yet stimulation of this 

 same anterior root produces extension. 

 And this agrees entirely with the results obtained in a different 

 way by Dr. Risien Russell ('Phil. Trans.,' 1893). 



The above experiment also goes to show that stimulation of one 

 posterior root causes impulses to pass out along many anterior roots. 



