Chap, ii.] THE BRAIN. 763 



cerebral surface to the endings of the strand in the cervical and 

 dorsal spinal cord. Nor can it be urged in such cases that 

 diffused remnants of the arm area had been left in the remain- 

 ing parts of the motor region ; for the whole motor region has 

 been removed, and yet the animal has recovered to such an 

 extent that a casual observer could detect no differences between 

 the movements of the two sides of the body. Closer examina- 

 tion did disclose certain imperfections of movement ; but the 

 operation had involved injury to or produced changes in struc- 

 tures other than the motor region, and the imperfections might 

 have been due to the additional damage. Nor can it be urged 

 that, in such a case, where "one side is removed, the remaining 

 hemisphere takes on double functions ; for the greater part of 

 the motor areas have been removed on both sides, and yet the 

 animal's movements have been so far apparently complete that 

 a casual observer would see nothing strange in them. Again, 

 the whole motor region has been removed from one hemisphere 

 in a young puppy, and some time later when the movements 

 seemed to have recovered their normal condition, the removal 

 of the motor region of the other hemisphere has produced 

 merely a 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 dis- 

 appearance or at least to great diminution of them ; and this 

 affords an additional 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 im- 

 pulses, 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 



