1056 VOLUNTARY MOVEMENTS. [BOOK in. 



and what alone are the absolutely permanent effects of the loss of 

 a cortical area and nothing else. On the one hand, in the cases 

 in which recovery of a movement follows upon its loss or impair- 

 ment, it is open for us to suppose that the lesion itself was 

 temporary, and that with the cure of the malady the cortical area 

 regained its normal condition. On the other hand, where the 

 disease continues, the permanency of the loss of any movement 

 may be attributed to the disease doing more than merely suspend 

 the function of the cortical area. Aphasia, especially in young 

 persons, has been followed by recovery, but in such cases it has 

 been supposed that the dormant area on the right side has been 

 awakened to activity by the loss of the left area ; and in support 

 of this view cases have been recorded in which a first aphasia, due 

 to a lesion on the left side, has been followed by a second aphasia 

 * J -due to a sequent lesion occurring on the right side. On the 

 whole perhaps the evidence of clinical study tends to shew that 

 in man the loss of movement due to the destruction by disease 

 of an area is a permanent one, though actual demonstration of 

 this is wanting. 



660. We may now return to the discussion of the question, 

 what is the part played by a motor area, and by the contribution 

 from that area to the pyramidal tract in carrying out the move- 

 ments with which the area is associated ? 



We may premise that the evidence points very distinctly to 

 the conclusion that whatever be the nature of the whole chain of 

 events of which the cortical area seems to be a sort of centre, the 

 fibres of the pyramidal tract serve as the channel of processes 

 which we must regard as efferent in nature. It is perfectly true 

 that in many cases at least the removal of a cortical area has led 

 to diminished sensibility of the part in which movements are 

 excited by stimulation of the area ; and there are many facts, of 

 which we shall presently quote a very striking one, which go to 

 shew that the cortex of the motor region is largely influenced by 

 sensory impulses from various parts of the body ; but we cannot 

 suppose that the pyramidal tract is the channel by which such 

 sensory impulses reach the cortex. As we have previously ( 568) 

 urged, the fact that the degeneration of the fibres in the tract is 

 a descending one, cannot be trusted by itself to prove that the 

 direction in which the fibres carry impulses is only that from the 

 cortex downwards ; but this added to the fact that when the fibres 

 of the tract are stimulated at any part of their course, movements, 

 the signs of the occurrence of efferent centrifugal impulses, are 

 produced, leaves no doubt that the tract is one of efferent fibres. 

 Hence we may infer that whatever be the nature of the events 

 taking place in a motor area during the carrying out of a move- 

 ment, the part played by the fibres of the pyramidal tract is that 

 of carrying efferent impulses from the area to the muscles con- 

 cerned. 



