268 Mr. J. S. R. Russell. On the Nerve Roots of 



ments represented in the middle root of the series cancel each other, 

 as it were, so that neither predominates, as in the case of flexion and 

 extension at the ankle as represented in the 6th lumbar root. But 

 when the muscles producing the one movement predominate over 

 those producing the opposite one, in my experience those muscles 

 always predominate in that root, e.g., the flexors of the digits in the 

 6fch lumbar root. 



As regards the order in which flexion and extension at the various 

 joints are represented in their relationship to the spinal level, we 

 find the following to be the order in the fore limb of the dog. 



Flexion at the shoulder.* 

 Flexion at the elbow. 

 Extension at the shoulder. 

 Extension at the wrist. 

 Flexion at the wrist. 

 Extension at the elbow. 

 Extension at the digital joints. 

 Flexion at the digital joints. 



Thus, while flexion is represented at a higher level than extension for 

 the upper segments of the limb, the reverse obtains for the lower 

 segments of the limb. 



The following is the order of representation of these movements as 

 regards the spinal level in the posterior extremity of the dog and 

 monkey : 



Flexion at the hip. 



Extension at the knee. 



Flexion at the ankle. 



Extension at the digital joints. 



Flexion at the knee. 



Extension at the hip. 



Extension at the ankle. 



Flexion at the digital joints. 



Here the arrangement as regards the segments of the limb is an 

 alternate one, flexion of the highest segment coming first, then exten- 

 sion of the next segment ; while for the lower segments flexion again 

 comes first, and is followed by extension for the next or terminal 

 segment of the limbs. 



So that in comparing the order of representation of movements of 

 the posterior with that of the anterior extremity it is found that the 

 highest segments coincide by having flexion as the highest represen- 

 tation, but that none of the other segments thus coin cide, until the 



* For purposes of comparison the forward movement of the limb at the shoulder 

 joint is called flexion, while the backward movement is called extension. 



