ASSOCIATED MOVEMENTS. 8T 



movements of one hand, while an entirely different order of 

 movements is executed by the other ; and instances of this 

 kind might be multiplied. 



In studying these associated movements, the question 

 arises as to how far they are due to the anatomical relations 

 of the nerves to the centres and their connections with mus- 

 cles, and how far they depend upon habit and exercise. "We 

 can imagine that there are certain sets of nerve-cells, con- 

 nected with each other by commissural fibres and giving ori- 

 gin to motor nerves distributed to sets of muscles ; an ana- 

 tomical arrangement that might render a separate action of 

 these cells impossible. The anatomy of the nerve-centres 

 and their connection with fibres are so difficult of investiga- 

 tion, that demonstrative proof of the existence of such sys- 

 tems is impracticable ; but this affords a ready explanation 

 of the fact that we cannot, as a rule, by an effort of the 

 will, cause a portion only of a single muscle to contract ; yet 

 some of the larger muscles receive an immense number of 

 motor nerve-fibres which are probably connected with gray 

 matter composed of numerous anastomosing cells. 



Many of the associated movements are capable of being 

 influenced to a surprising degree by education, of which no 

 better example can be found than in the case of skilful per- 

 formers upon certain musical instruments, such as the piano, 

 harp, violin, and other stringed instruments. In the tech- 

 nical study of such instruments, not only does one hand be- 

 come almost independent of the other, but very complex 

 associated movements may be acquired. An accomplished 

 pianist or violinist executes the different scales automati- 

 cally by a single effort of the will, and frequently pianists 

 execute at the same time scales with both hands, the action 

 being entirely opposed to the natural association of move- 

 ments. Feats of sleight of hand also show how wonderfully 

 the muscles may be educated, and to what an extent the 

 power of association and disassociation of movements may 

 be acquired by long practice. 



