726 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



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 an 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 particular 

 movement, may seem to derive some support from the sense of 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 indication 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. 



755. There are two cases 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 these 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 re- 

 marked, not by the muscular sense, but by the visual and auditory senses respect- 

 ively. 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 determi- 

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

 eyeball to roll in a given direction, in accordance with a visual sensation; 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 side or the other, we 

 feel that we can do so but very imperfectly, and with a sense of effort referred 

 to the muscles themselves, this sense being the result of the state of tension 

 in which the muscles are placed, by the effort to move the eyes without the 

 guiding visual sensation. Now, on the other hand, the Will may determine to 

 fix the eyes upon an object; and yet this very fixation may be only attainable 

 by a muscular movement, which movement is directly excited by the visual 

 sense, without any exertion of voluntary power over the muscles. Such is the 

 case when we look steadily at an object, whilst we move the head horizontally 

 from side to side; for the eyeballs will then be moved in the contrary direction 

 by a kind of instinctive effort of the external and internal recti, which tends to 

 keep the retinae in their first position, and to prevent the motion of the images 

 over them. So, when we look steadily at an object, and incline the head towards 

 either shoulder, the eyeballs are rotated upon their antero-posterior axis (proba- 

 bly by the agency of the oblique muscles) apparently with the very same pur- 

 pose, that of preventing the images from moving over the retinae. Now we 

 cannot refuse to this rotation any of the attributes which really characterize the 

 so-called voluntary movements; and yet we are not even informed by our own 

 consciousness that such a movement is taking place, and know it only by ob- 

 servation of others. 



756. The muscular contractions which are concerned in the production of 

 vocal tones are, in like manner, always accounted voluntary; and yet it is easy 

 to show that the Will has no direct power over the muscles of the larynx. For 

 we cannot raise or depress the larynx as a whole, nor move the thyroid cartilage 

 upon the cricoid, nor separate or approximate the arytenoid cartilages, nor ex- 

 tend or relax the vocal ligaments, by simply willing to do so, however strongly. 

 Yet we can readily do any or all these things by an act of the Will exerted for 

 a specific purpose. We conceive of a tone to be produced, and we will to pro- 

 duce it; a certain combination of the muscular actions of the larynx then takes 



