Causation of \ital Movement. 



439 



Fig. 8. 



nerve-endings are confined to very small spots which we term fields 

 of innervation. Most muscle-fibres have only one field of innervation, 

 very long ones occasionally several, at the most eight. Thus the 

 assumption, opposed to the idea of independent irritability, that 

 muscle substance is well-nigh completely riddled with nerves, is 

 refuted and rejected from the morphological side also. 



From the absence of nerves in long tracts of muscle-fibre we im- 

 mediately conclude that the latter shares with nerves the faculty of 

 independently propagating its own excitation. This is what the beau- 

 tiful microscopic observations of Sir William Bowman (15) on insects' 

 muscles long since led us to suspect. As in the nerve so in the muscle, 

 conduction takes place in every direction, and as the field of innerva- 

 tion almost without exception occupies a median position during a 

 normal contraction, the conduction takes place in both directions, 

 towards the tendinous ends. By way of distinction the velocity of 



