CHAP, ii.] THE BRAIN. 1051 



paralysis of the crossed side of the body, and that as before only 

 of a temporary character. 



Two things have to be noted here. In the first place the 

 removal of an area does affect the movements which are brought 

 about by stimulating that area, it leads to their disappearance or 

 at least to great diminution of them ; and this affords an addi- 

 tional argument that the connection between the area and the 

 movement is a real and important one. In the second place, the 

 physiological effect is temporary only, though the anatomical 

 results of the operation are permanent, for the cortex is never 

 renewed, and the pyramidal tract degenerates along its whole 

 length, never to be restored ; this shews that we have to deal here 

 with events of a very complex character. When a particular 

 movement results from stimulation of the appropriate cortical 

 area, we may be sure that whatever takes place in the cortex and 

 along the pyramidal tract, motor impulses, duly coordinated, pass 

 along certain anterior roots to certain muscles ; and we know that 

 if we removed a sufficient length of each of those anterior roots 

 that particular movement would be lost for the rest of the life of 

 the individual. We may therefore infer that the events which, 

 whatever be their exact nature, taking place in the cortex and 

 along the pyramidal tract lead ultimately to the issue of motor 

 impulses along the anterior roots, differ essentially from the events 

 attending the transmission of ordinary motor impulses. 



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 knowledge 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 com- 



