CHAPTER IX 

 DISCUSSION 



Discussion of muscle action and limb motion 



Investigation of the functions of muscles and analysis 

 of their actions is so beset with difficulties that it is im- 

 possible to do a great deal in this line with the lower mam- 

 mals by existing technique. Even in man, an investigation 

 of the actions of the deeper muscles is anything but easy, 

 and much more difficult in the case of other mammals. 

 We know what a muscle can do perhaps, by noting the 

 positions of origin and insertion, and further information 

 may be obtained by observations of action and by stimu- 

 lating a nerve electrically. But the important point is to 

 know the part that it plays in action of muscle groups, and 

 this can rarely be ascertained. 



When we give thought to the matter it is seen that even 

 such a simple act as scratching one's ear is, in reality, 

 exceedingly involved. Then too, the same act may be 

 simple or complex. Thus, the opening of a drawer may 

 necessitate merely the flexion of a finger and then of the arm, 

 or if the drawer sticks, it may be necessary to bring into 

 play most of the muscles of the body. One must consider 

 that the precise method by which an action is controlled is 

 unknown. We may stretch forth an arm merely to touch 

 the most fragile object or to fell an enemy. We may know 

 that a muscle is an extensor of a certain part, but we do not 

 know under just what conditions it may or may not act as 

 such. 



It is beyond the province of the present paper to present 

 in detail what is known of muscle structure and the physio- 

 logical manner in which action is accomplished. Certain 



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