1062 VOLUNTARY MOVEMENTS. [BOOK m. 



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 mechan- 

 ism as in the case of the unskilled 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 ( 591). Lesions of the pyramidal system, of the internal 

 capsule for instance, lead to the loss not only of skilled but of all 

 voluntary movements ; 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 the lesion this or that part of the body is wholly withdrawn from 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 pyramidal 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 con- 

 stituting 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 perhaps 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 grey matter, 

 which serves as a set of nuclei of origin for the motor nerves con- 

 cerned 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 cere- 

 bellum thereby be troubled, or mischief fall on some other part 

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

 the pyramidal tract or the motor cortex, the movement fails 

 through lack of coordination, though both the cortex, the pyra- 



