ON VOLUNTARY MOVEMENTS. 683 



is nearly but not quite complete ; the " will " can gain access to the right 

 hand, but not so easily as to the left hand, and this latter is used, though 

 under ordinary circumstances it would not be used. 



When we turn to man, in whom the great development of the pyramidal 

 system and differentiation of the cortical area is paralleled by the promi- 

 nence of skilled and trained movements, the analogy of the phenomena of 

 speech, if it be true, as clinical histories seem to show, that destruction by 

 disease of the speech area of both sides causes permanent aphasia, would 

 lead us to conclude that at least highly skilled voluntary movements are 

 carried out by the pyramidal system and by that alone. But in reference to 

 this it must be remembered that such a permanent aphasia may be due, not 

 to mere loss of the pyramidal channel, not to the will being merely unable 

 to gain access to lower coordinating mechanisms, but to the absence of the 

 differentiated cortical gray matter, by reason of which absence the will can- 

 not initiate the first processes of the act of speech ; it may be that were it 

 able to do so, the processes so started might, in the absence of the pyramidal 

 tract, find some other way to the bulbar mechanism, as in the case of the un- 

 skilled movements of the dog. This point, however, clinical histories have 

 not definitely settled. Moreover, in dealing with the phenomena of the 

 nervous system of man, as revealed by disease, we meet in reference to the 

 cerebral cortex the same difficulty that we dwelt upon in dealing with the 

 spinal cord ( 504). Lesions of the pyramidal system, of the internal capsule 

 for instance, lead to the loss not only of skilled, but of all voluntary move- 

 ments ; according to the character and position of the lesion this or that part 

 of the body is wholly withdrawn from the influence of the will. And it is 

 possible to maintain the thesis that man has become so developed as to his 

 nervous system and the motor cortex, so accustomed to make use exclusively 

 of the pyramidal system, that the will has lost the power, still possessed by 

 lower animals, to gain access by some path other than the pyramidal one to 

 the immediate nervous mechanisms of movement. The data for forming a 

 satisfactory conclusion as to this point are so few and uncertain that it would 

 be unprofitable to discuss the question here ; but we may venture to point out 

 that, great as is the development of the cerebral cortex and the pyramidal 

 system in man, that development is accompanied by a hardly less striking 

 expansion of other parts of the brain not directly connected with the pyram- 

 idal system which we have previously seen reason to associate with the 

 coordination of movements, for example the cerebellum. And, indeed, it is 

 clear that, admitting the pyramidal tract to be the ordinary channel by 

 which volitional impulses pass to, or by which the will gains access to, the 

 motor mechanisms immediately associated with the anterior roots of this or 

 that spinal nerve, we must also admit that those volitional impulses passing 

 along the pyramidal tract, or at least some of the processes constituting the 

 will, are in connection with, and thus are influenced by the condition of, 

 other parts of the brain. When, for instance, a gymnast executes a skilled 

 voluntary movement in which all his four limbs and other parts as well per- 

 haps of his body are involved, it is probably the case that changes of the 

 nature of efferent impulses sweep down his pyramidal tract, and that these 

 impulses, starting in a definite order from his cortex, that is to say, having 

 undergone a certain amount of initial coordination at their very origin, meet 

 with further coordination in the spinal gray matter, which serves as a set of 

 nuclei of origin for the motor nerves concerned in the movement before they 

 issue as ordinary motor impulses along the anterior roots. But this is not 

 all. Should the gymnast's semicircular canals happen to be injured and his 

 cerebellum thereby be troubled, or mischief fall on some other part of the 

 brain which like this has no direct connection with either the pyramidal 



