1068 VOLUNTARY MOVEMENTS. [BOOK in. 



mechanisms. In the dog we may conclude that in voluntary 

 movements the spinal mechanisms, with coordinating functions, 

 are also set in action, in this case by impulses passing straight 

 from the cortex to the mechanisms by the pyramidal tract, 

 though apparently, in the absence of the pyramidal tract, the 

 will can work upon the mechanisms by changes travelling 

 through other parts of the cerebrospinal axis. And in the 

 monkey and man, subject to the doubts already expressed as to 

 the potentialities of the human spinal cord, we may probably also 

 infer that in each voluntary movement some, perhaps we may say 

 much, of the coordination is carried out by the spinal mechanism 

 set into action through impulses along the pyramidal tract. We 

 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 

 effected, 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 shewn 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 well 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, 632, fibres pass to the pons to make connections with the 

 cerebellum. On the other hand, as we have seen, 612, the cere- 

 bellum 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 coordinating 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 



