16 TEANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



root is a collection gathered together for a functional 

 purpose, and representing a particular highly co-ordinated 

 movement of the limb. Contrary to any such hypothesis, 

 it shews that for the functional mechanism of the limb 

 it is immaterial whether this or that particular group 

 of muscles is represented in a particular spinal root or 

 not represented in it. The absolute segmental level is 

 variable over the range of nearly a whole segment's 

 length ; the relative segmental position is, however, 

 inviolably preserved. Thus flexor carpi uluaris may get 

 fibres from as high as the 6th cervical segment, or it may 

 not, but it never extends so well forward, so far rostrally, 

 as flexor carpi radialis, and this latter never extends so 

 far aborally as flexor carpi uluaris, even when it is most 

 post-fixed; that is the region of out-flow for the spinal 

 nerve-fibres to flexor carpi uluaris lies rather more aborally 

 than that of the out-flow of flexor carpi radialis, and this 

 mutual segmental position of the muscles is maintained 

 whether the plexus be post-fixed or pre-fixed. 



The idea at root of the supposition, that the motor-root 

 is a functional collection of nerve-fibres, seems to be that 

 juxta-position in space is advantageous for co-ordination 

 of action. The material of support for this idea is very 

 slender, and there are many facts which show that mere 

 spatial separation offers no difficulty for the physiological 

 mechanism of co-ordinate and synchronous activity. The 

 great respiratory centre in the spinal bulb, and the various 

 subsidiary spinal respiratory centres, lie very far remote 

 one from another. Yet how accurately do they harmonise 

 in their activity? Their co-ordination consists rather in 

 the fact that they are all chemically tuned, so to say, to 

 the same pitch or note of stimulus. They differ from all 

 the other bulbo-spinal centres, and agree among themselves 

 in their peculiar sensitivity to the stimulus of venous 



