670 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



Cerebrum may thus call the motor apparatus into action, as the instrument 

 either of ideas, of emotions, or of volitional determinations; but we must limit 

 our present examination to voluntary movements alone, these having been 

 usually regarded as in such complete antagonism to those of the automatic 

 group, that even separate sets of nerve-fibres have been thought requisite to 

 account for the transmission of these two distinct orders of motor impulses 

 to the muscles. 



540. Now, in the first place, it may be asserted, with some confidence, that 

 no effort of the Will can exert that direct influence on the muscles, which 

 our ordinary phraseology, and even the language of scientific reasoners, 

 would seem to imply ; but, on the other hand, that the Will is solely con- 

 cerned in determining the result; the selection and combination of muscular 

 movements required to bring about this result, not being effected by the Will, 

 but by some intermediate agency. If it were otherwise, we should be de- 

 pendent upon anatomical knowledge for our power of performing the sim- 

 plest movement of the body ; whereas we find the fact to be, that the man 

 who has not the least idea of the mechanism of muscular action, can acquire 

 as complete a command over his movements, and can adapt them as perfectly 

 to the desired end as the most accomplished anatomist could do. Further, 

 we cannot, by any exertion of the will, single out a particular muscle, and 

 throw it into contraction by itself, unless that muscle be one which is alone 

 concerned in an action that we can voluntarily perform ; and even then we 

 single it out by willing the action. Thus we can put the levator palpebrce in 

 action by itself; but this we do not by any conscious determination of power 

 to the muscle itself, but by icttling to raise the eyelids ; and it is only by our 

 anatomical knowledge that we know that but a single muscle is concerned 

 in this movement. So far as our own consciousness can inform us, there is 

 no difference between the mechanism of this action and that of the flexion 

 of the knee- or elbow-joint; and yet in these latter movements several 

 muscles are concerned, not one of which can be singled out by any effort of 

 the will, and thrown into action separately from the rest. The idea that the 

 will is directly exerted upon the muscles called into action to produce a par- 

 ticular movement, may seem to derive some support from the sense of mus- 

 vulnr effort of which we are conscious in making the exertion, and which we 

 refer to the muscles which are concerned in it; but this sense of effort is 

 nothing else than the "muscular sense" already alluded to, which has its 

 origin in the state of tension of the muscles, and which is no more an indi- 

 cation of mental effort directed to them, than the sensation of light or sound 

 is an indication of a determination of voluntary power to the eyes or ears. 



541. There are two cases, already referred to under another head, in 

 which it is very easy to show that the Will is concerned with the result alone, 

 and is not directly exerted upon the instruments by which that result is 

 brought about: these are, the movements of the Eyes, and the production 

 of Vocal tones. In neither of them are we conscious of any effort in the 

 muscular apparatus, unless the contraction be carried beyond its accustomed 

 extent; the ordinary movements being governed, as already remarked, not 

 by the muscular sense, but by the visual and auditory senses respectively. 

 Nothing can be more simple, to all appearance, than the act of turning the 

 eyes upwards or downwards, to one side or the other, in obedience to a 

 determination of the Will ; and yet the Will does not impress such a deter- 

 mination upon the muscles. That which the Will really does, is to cause 

 the eyeballs to roll in a given direction, in accordance with a visual sensa- 

 tion ; and it is only when there is an object towards which the eyes can be 

 turned, that we can move them with our usual facility. When the eyelids 

 are closed, and we attempt to roll the globes upwards or downwards, to one 



