1050 REMOVAL OF CORTICAL AREAS. [BOOK in. 



mind that it appears to govern, and must therefore be bound by 

 close ties to almost all the rest of the central nervous system, we 

 must be prepared to find after removing a portion of cortex that 

 the pure 'deficiency' phenomena, those which result from the 

 mere absence of a piece of the cortex, are largely obscured by 

 the other effects of the operation. 



In the rabbit the results have been almost purely negative. 

 When in this animal the part of the cortex which may be con- 

 sidered as the motor region 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 operated 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 com- 

 pletely or partially 'paralysed.' 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 deviation from the normal use. And 

 careful examination after death has shewn 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 pyra- 

 midal 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 diffused 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 move- 

 ment ; but the operation had involved injury to or produced 

 changes in structures other than the motor region, and the imper- 

 fections 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 



