2% ON CUTANEOUS AND [BOOK in. 



more accurate judgments concerning the weight of the object 

 than when we rely on sensations of pressure alone. When we 

 want to tell how heavy a thing is, we are not in the habit of 

 allowing it simply to press on the hand laid flat on a table or 

 otherwise at rest ; we hold it in our hand and lift it up and 

 down. 



The above instances deal with three things which it might be 

 desirable to keep separate, namely, ' position,' ' movement ' and 

 ' effort ; ' it might seem desirable to speak of " a sense of position," 

 " a sense of movement," and " a sense of effort." But, if we leave 

 out of consideration the problems connected with our appreciation 

 of the position of the head, which as we have seen seems especially 

 dependent on afferent impulses passing up the auditory (vestibular) 

 nerve, we may say that the position of the various parts of our 

 body is so closely dependent on movement, that is on the contrac- 

 tion of skeletal muscles, some muscle or other playing its part in 

 almost every position and every change of position, that in the 

 discussion on which we are now entering it will be hardly profit- 

 able to distinguish between the two ; and we may use the term 

 " muscular sense " to denote our appreciation both of movement 

 and of position resulting from movement. 



892. There are more valid reasons for distinguishing between 

 our appreciation of an effort and our appreciation of the movement 

 which is the result of that effort. For the view has been put 

 forward and supported by argument that when we make a mus- 

 cular effort, we are directly conscious of the nervous processes 

 of the central nervous system underlying the effort, that the 

 changes in the central nervous system involved in initiating and 

 executing a movement of the body so affect our consciousness 

 that we have a sense of the nervous effort itself, of the innervation 

 as it has been called ; and it is urged that the condition of the 

 central nervous system through which we appreciate the nature 

 and magnitude of the effort is thus the direct effect of central 

 changes, and not the outcome of afferent impulses proceeding 

 from the part moved. 



Whether it be the case or not that consciousness is thus directly 

 affected by changes in the central nervous system, such for 

 instance as those taking place in the motor cortical area or in 

 the pyramidal tract, the evidence goes to shew that any such 

 affection has, at most, very little share in that appreciation of our 

 movements which is generally called " the muscular sense." Not 

 only is our appreciation of passive movements very similar to our 

 appreciation of active movements (we are as well aware of an 

 attitude in which our arm has been placed by others as of one 

 in which we have placed it ourselves), but also if a muscular 

 contraction be brought about not by any action at all of the 

 central nervous system, but by the direct electric or other 

 stimulation of the muscles or motor nerves, the muscular sense 



