674 THE BRAIN. 



is removed, nothing remarkable is observed in the movements of the animal 

 We can hardly suppose that the operations of the central nervous system are 

 the same in an injured as in an intact animal, and the differences induced 

 ought to be betrayed by the movements of the body ; but at present they 

 have escaped observation. 



In the dog the removal of an area is followed by a loss or diminution of 

 voluntary movement in the corresponding part of the body. When, for 

 instance, the area for the fore limb is removed from the left hemisphere, the 

 right fore limb is completely or partially " paralyzed." In carrying out its 

 ordinary movements the operated animal makes little or no use of its right 

 fore limb. But this state of things is temporary only. After a while the 

 animal regains power over the limb, and in successful cases recovery is so 

 complete that it is impossible to point out in the limb any appreciable devia- 

 tion from the normal use. And careful examination after death has shown 

 not only that the area had been wholly removed, but also that there was no 

 regeneration of the lost parts ; the removal of the cortex leads in such cases, 

 as usual, to degeneration of the corresponding strand in the pyramidal tract 

 right away from the cerebral surface to the endings of the strand in the 

 cervical and dorsal spinal cord. Nor can it be urged in such cases that dif- 

 fused remnants of the arm area had been left in the remaining 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 

 examination did disclose certain imperfections of movement ; but the opera- 

 tion had involved injury to or produced changes in structures other than 

 the motor region, and the imperfections might have been due to the addi- 

 tional 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 tem- 

 porary 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 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 shows 

 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 ante- 

 rior 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. 



