1014 MACHINERY OF COORDINATION. [BOOK in. 



are at work, determining such coordination as is present. In such 

 a case the coordinating afferent impulses are relatively simple 

 in character and start chiefly at all events in the muscles con- 

 cerned. In an animal possessing the lower parts of the brain, 

 though deprived of the cerebral hemispheres, the coordinating 

 afferent impulses, in accordance with the greater diversity and 

 complexity of the movements which the animal is able to execute, 

 are far more potent and varied. Besides afferent impulses from 

 the muscles, forming the basis of what we have called the muscular 

 sense, afferent impulses from the skin, forming the basis of the 

 sense of touch in the wide meaning of that word, other afferent 

 impulses of obscure character from the viscera and various tissues, 

 and the peculiar afferent ampullar impulses of which we have just 

 spoken, important special afferent impulses borne along the nerves 

 of sight and hearing come into play. The frog, the bird, and even 

 the mammal, deprived of the cerebral hemispheres, though it may 

 shew little signs or none at all of having a distinct volition, is as 

 we have urged indubitably affected by visual and auditory 

 impressions, and whether we admit or no that such an animal 

 can rightly be spoken of as being conscious we cannot resist the 

 conclusion that afferent impulses started in its retina or internal 

 ear produce in its central nervous system changes similar to those 

 which in a conscious animal form the basis of visual and auditory 

 sensations, and we must either call these changes sensations or 

 find for them some new word. Whatever we call them, and 

 whether consciousness is distinctly involved in them or no, they 

 obviously play an important part as factors of the coordination 

 of movements. Indeed, when we appeal to the experience of 

 ourselves in possession of consciousness, we find that though 

 various sensations clearly enter into the coordination of our 

 movements, we carry out movements thus coordinated without 

 being distinctly aware of these coordinating factors. In every 

 movement which we make the coordination of the movement is 

 dependent on the impulses or influences which form the basis 

 of the muscular sense, yet we are not distinctly conscious of 

 these impulses ; it is only as we shall see by special analysis 

 that we come to the conclusion that we do possess what we 

 shall call a muscular sense. So again, taking the matter from 

 a somewhat different point of view, many of our movements, 

 markedly as we shall see those of the eyeballs, are coordinated 

 by visual sensations, and when we sing or when we dance to 

 music our movements are coordinated by the help of sensations 

 of sound. In these cases distinct sensations in the ordinary sense 

 of the word intervene ; if we cannot see or cannot hear, the 

 movement fails or is imperfect : yet even in these cases we are 

 not directly conscious of the sensations as coordinating factors ; it 

 needs careful analysis to prove that the success of the movement 

 is really dependent on the sound or on the sight. These and 



