688 THE BRAIN. 



may probably further infer that a careful adjustment obtains between the 

 beginnings of the pyramidal tract in the cortex and its endings in the cord, 

 so that the topography of " areas " or " foci " in the cortex above is an image 

 or projection of the spinal mechanisms below. 



The complex character, on which we insisted just now, of almost every 

 voluntary movement necessitates that in every such movement a large area 

 of spinal mechanism is involved. But this is not all. The movements of 

 any part of the legs, for instance, are not determined, nor is the coordination 

 of the movements affected, simply by what is going on in the legs and the 

 part of the spinal cord belonging to them. The discussion in a previous 

 section has shown that much of the coordination of the body is carried out 

 by the middle portions of the brain, and on these the motor area must have 

 its hold as on the spinal mechanisms. 



The details of the nature of that hold are at present unknown to us ; but 

 it must be remembered that not all the fibres passing down from the motor 

 region, not all those even proceeding from the densest and most clearly 

 defined motor areas, are pyramidal fibres. With the pyramidal fibres are 

 mingled fibres having other destinations, and some of these probably pass 

 to the thalamus and so join the great tegmental region. Moreover, the 

 motor region must have close ties with other regions of the cortex whence, as 

 we have seen ( 545) fibres pass to the pons to make connections with the 

 cerebellum. On the other hand, as we have seen ( 525) the cerebellum is 

 especially connected with what we may fairly consider the afferent side of 

 the spinal cord and bulb. These facts must merely be taken as indicating the 

 possibilities by which the motor region is kept in touch with the great coordi- 

 nating mechanism ; it would be venturesome at present to say much more. 



In an ordinary voluntary movement an intelligent consciousness is an 

 essential element. But many skilled movements initiated and repeated by 

 help of an intelligent conscious volition may, when the nervous machinery 

 for carrying them out has acquired a certain facility (and in all the higher 

 processes of the brain we must recognize that, in nervous material at all 

 events, action determines structure, meaning by structure molecular arrange- 

 ment and disposition), be carried out under appropriate circumstances with 

 so little intervention of distinct consciousness that the movements are then 

 often spoken of as involuntary. All the arguments which go to show that 

 the distinctly conscious voluntary skilled movement is carried out by help 

 of the appropriate motor area go to show that the motor area must play its 

 part in these involuntary skilled movements also. So that distinct con- 

 sciousness is not a necessary adjunct to the activity of a motor area. And 

 it is worthy of notice that some of these, in their origin, purely voluntary 

 skilled movements, which by long-continued training have become almost 

 as purely involuntary, are hampered rather than assisted by being " thought 

 about." ' 



The word " training " suggests the reflection that the physiological inter- 

 pretation of becoming easy by practice is that new paths are made, or the 

 material of old paths made more mobile by effort and use. We have already 

 urged ( 494) that the gray matter of the spinal cord is a network, in which 

 the passage of impulses is determined by physiological conditions rather than 

 anatomical continuity, and the same considerations may with still greater 

 force be applied to the brain. We must suppose that training promotes the 

 growth and molecular mobility of the motor area and of all its connections. 

 There are doubtless limits to the changes which can be effected, but within 

 these limits the will, blundering at first in the maze of the nervous network, 

 gradually establishes easy paths ; though even to the end it blunders in 

 trying to carry out one movement it often accomplishes another. 



