1060 OK CUTANEOUS AND [BOOK m. 



of effort needed to lift an object as well as to sensations of 

 pressure, we can form much more accurate judgments con- 

 cerning 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, c 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 contraction 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 profitable to dis- 

 tinguish between the two ; and we may use the term " muscular 

 sense " to denote our appreciation both of movement and of 

 position resulting from movement. 



660. 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 muscular 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 



