the Lwnbo-Sacral Plexus of Macacus rhesus. 259 



detectable, but here again the experiment has not been repeated 

 sufficiently frequently in the type of monkey in which, according to 

 Sherrington, the 2nd sacral root supplies a branch to the sciatic 

 nerve, which supplies the intrinsic muscles of the foot. 



In no case did section of the 1st and 2nd lumbar roots cause any 

 impairment in the movements of the limb, nor did section of the 2nd 

 and 3rd in combination. When the 3rd and 4th lumbar roots were 

 divided on the same side, flexion at the hip was greatly impaired. 

 Movements at the knee appeared most affected when the 4th and 5th, 

 or 6th and 7th, lumbar roots were divided together on the same side, 

 roots which, as we have seen from the stimulation experiments, are 

 concerned with the movements at the knee. The division of the last 

 two roots mentioned also produced most effect on the movements at 

 the ankle. The movements of the digits were most affected when 

 the 7th lumbar and 1st sacral roots were divided together, roots 

 excitation of which produced these movements. Section of the alter- 

 nate roots, 3rd and 5th, 4th and 6th, 5th and 7th, 6th lumbar and 1st 

 sacral, in combination, produced very little effect. In some cases it 

 was possible to detect slight impairment of movements, but in others 

 it was extremely difficult to be sure that there was any. If, however, 

 three alternate roots, such as the 3rd, 5th, and 7th lumbar, or the 4th 

 and 6th lumbar and 1st sacral, were divided together on the same 

 side, there was no difficulty in detecting the general impairment of 

 the movements of the limb. 



In every case there was rapid improvement. In some this was so 

 great that it was difficult to be certain that any impairment of move- 

 ment remained, notably where alternate roots had been divided. In 

 others, while most of the movements seemed as well performed as 

 on the opposite side, impairment of a particular movement at a given 

 joint remained, this being the case where two or more consecutive 

 roots had been divided. 



These results are in keeping with those which were obtained in 

 connexion with the cervico-dorsal nerve roots of the dog. As in 

 those experiments, reunion of the divided ends of the nerve roots was 

 not the cause of the improvement in motor power, as there was not 

 the slightest sign of any such reunion on post-mortem examination, 

 and I have no other explanation to offer for the improvement in 

 motor power which occurs, other than one of the hypotheses formerly 

 advanced in explanation of the phenomenon. One of these suggested 

 the possibility of a reflex inhibitory effect on the cells of the cortex 

 cerebri by the section of a nerve root or roots, producing at first a 

 greater degree of paralysis than would result from exclusion of the 

 nerve root alone. The other supposed it possible that cortical im- 

 pressions travelling down to the limb and meeting with a block, 

 owing to the division of the fibres along which they formerly passed, 



