CHAP. XXVI.] VOLUNTARY MOVEMENTS. 555 



into the middle of which, unknown to him, a heavy leaden weight 

 had been introduced, his initial determination of the Movement 

 deemed to be adequate would need rectification, and in such a case 

 it would certainly be rectified in the main at the instigation of 

 Kinassthetic Impressions. 



Hitherto reference has heen made to the simpler class of Volun- 

 tary Movements to those in which the movements themselves ai'e 

 familiar or easy of execution. But where the movements which it 

 is desired to execute are complex and difficult, and we have to learn 

 them by imitation of the movements of other persons, the sense 

 of Sight is then doubly brought into play. It is necessary at the 

 commencement, and during the continuance, of our efforts to 

 copy such movements, to look alternately at our model and at 

 our own moving members. A long time and much practice is, iu 

 fact, required before a person learning to dance, or to play upon 

 some musical instrument, is able to execute either of these actions 

 without the aid from moment to moment of guiding Sight impres- 

 sions. "In learning to dance," as Hartley says, "the scholar 

 desires to look at his feet and legs, in order to judge, by seeing, 

 when they are in a proper position. By degrees he learns to judge 

 of this by feeling; but the visible idea left partly by the view of 

 his master's motions, partly by that of his own, seems to be the 

 chief associated circtimstance that introduces the proper motions." 

 During the process of learning, therefore, the Visual Centre evi- 

 dently exercises a dominating influence. 



In time, however, the impressions pertaining to the ' Sense of 

 Movement ' (which are, of course, always to some extent associated 

 with those of Sight) become, by way of their organized channels, 

 sufficiently freely associated with them and with the newly organ 

 izing ' motor ' nerve channels and mechanisms, to permit the Move- 

 ments we have been practising to be performed under the immediate 

 guidance of Kinaesthetic Impressions only without further neces- 

 sity for a conjoint direction through the sense of Sight. As Jaccoud, 

 however, points out (Les paraplegies et I'ataxie, p. 601) the 

 sensorium requires to learn, in the first instance, what conditions 

 and positions of the moving parts are related to such and such 

 tactile and other impressions coming from them, And thus it is 

 only at the termination of this apprenticeship that it is enabled to 

 conclude directly from Kinaesthetic Impressions as to the precise 

 conditions of the moving parts. This process of education can only 

 proceed correctly by reason of the comparisons which we are accus- 

 tomed to make from moment to moment, between the positions and 



