ON VOLUNTARY MOVEMENTS. 675 



In the case of the monkey, the results of removing parts of the cortical 

 motor region have not been so accordant as in the case of the dog. The 

 two animals agree perfectly in so far that the removal of a particular area 

 leads, as an immediate result, to the loss of the corresponding movement ; 

 but while in some instances recovery of the movement has in the monkey as 

 in the dog after a while taken place, in other instances the " paralysis " has 

 appeared to be permanent. As a rule the paralysis caused by a large lesion 

 is not only more extensive, but also of longer duration than that caused by 

 a small one ; and natural bilateral movements, as of the eyes, reappear 

 earlier than unilateral movements. The facts, however, within our know- 

 ledge relating to the permanence of the effect are neither numerous nor exact 

 enough to justify at present a definite conclusion. On the one hand, the 

 positive cases where recovery has taken place are of more value than the 

 negative ones, since in the latter the recovery may have been hindered by 

 concomitant events of a nature which we may call accidental ; and it is at 

 least a priori most unlikely that the pyramidal tract mechanism, if we may 

 use the expression, though it may differ in the monkey and the dog in degree 

 of development, differs so essentially in kind that damage of it leads in the 

 one case to permanent, and in the other to mere temporary, loss of function. 

 We may add that we should further expect to meet in the monkey with 

 more prominent and more lasting complications due to the subsidiary effects 

 of the operation, and it may be doubted whether in any of the recorded 

 experiments the animal has been allowed to live a sufficient time for these 

 subsidiary events to have cleared away, leaving only what we have called 

 the " deficiency" phenomena, due to the loss of the cortical area alone. On 

 the other hand, it must be remembered that the movements of the monkey 

 are more intricate in origin, more " skilled," than those of the dog ; and it 

 may be that differences in the characters of movements determine the possi- 

 bility of their recovery. In illustration of this we may quote the expe- 

 rience that, after the removal of the arm area in the monkey, a certain 

 awkwardness in the movements of the thumb is one of the last effects of the 

 operation. 



572. Before we proceed, however, any further in the discussion, it will 

 be of advantage to turn aside to what is known concerning the cortical 

 motor region in man. As we have already said, theoretical considerations 

 lead us to believe that the cortical motor region in man is disposed in accord- 

 ance with the plan of the anthropoid ape as ascertained experimentally, but 

 with the differentiation carried still further ; and the few cases of experi- 

 mental stimulation of the human cortex support this view. Our chief 

 knowledge in this matter is derived from the study of disease ; and in this 

 the advantages of dealing with one of ourselves are largely counterbalanced 

 by the disadvantages due to disease being so often anatomically diffuse and 

 physiologically changeful and progressive. 



We said above that during experiments on animals stimulation of any 

 part of the motor region may under abnormal conditions lead to general 

 epileptiform convulsions. Now clinical study has shown that in man certain 

 kinds of epileptic attacks are of similar cortical origin. In these cases it 

 has been observed that the attack begins in a particular movement, by con- 

 tractions of particular muscles or of the muscles of a particular region of 

 the body, of the hand, foot, toe, thumb, etc., and then spreads in a definite 

 order or " march " over the muscles of other regions until the whole body is 

 involved. When in an experiment on an animal epileptiform convulsions 

 supervene, they similarly start from the region of the body, the motor area 

 of which is beneath the electrodes at the time, and similarly spread by a 

 definite " march " over the whole body. Hence, in the human epileptiform 



