684 THE BRAIN. 



tract or the motor cortex, the movement fails through lack of coordination, 

 though both the cortex, the pyramidal tract, and the spinal motor mechan- 

 isms remain as they were before. Obviously the carrying out of a voluntary 

 movement is a very complex proceeding, and the motor cortex with the 

 pyramidal tract is only one part of the whole mechanism ; so far from the 

 whole business being confined to these, it is perhaps no exaggeration to say 

 that in each movement of the kind most parts of the whole brain have a 

 greater or less share. 



The exact nature of the part played by the cortex and the pyramidal 

 tract in voluntary movements our present knowledge is inadequate to define. 

 When we pass in review a series of brains from the lower to the higher and 

 see how the pyramidal system is, so to speak, grafted on to the rest of the 

 brain, when we observe how the increasing differentiation of the motor cor- 

 tex runs parallel to the increasing possession of skilled educated movements, 

 we may perhaps suppose that a " short cut " from the cortex to the origins 

 of the several motor nerves, such as is afforded by the pyramidal fibres, 

 from the advantages it offers to the more primitive path from segment to 

 segment along the cerebro-spinal axis has by natural selection been developed 

 into being in man the chief and most important instrument for carrying out 

 voluntary movements ; but, we repeat, it remains even in its highest develop- 

 ment a link in a chain, and a knowledge of how the whole chain works is 

 at present hidden from us. 



We must not here wander into psychological problems, but may repeat 

 that in the above discussion we have used the word "will" in a general 

 sense only. A man maybe brought into a condition, for instance in certain 

 hypnotic phases, in which he can carry out all the various skilled movements 

 which he has inherited or which he has learned ; and yet, according to some 

 definitions of the word " will," those movements could not be said to be initi- 

 ated by his will. It can hardly be doubted that in such cases the motor 

 cortex and pyramidal tract play their usual part. But we may pass from 

 such cases as these through others, until we come to cases where a skilled 

 movement which has been learned and practised by the working of an in- 

 telligent will, may continue to be carried out under circumstances which 

 seem to preclude the intervention of any conscious will at all ; and the 

 transition from one case to another is so gradual, that it is impossible to sup- 

 pose that there has been any shifting of the machinery employed for carry- 

 ing out the movement. So that a volitional origin is not an essential feature 

 of these so-called voluntary movements, and the machinery of the motor 

 cortex and pyramidal tract is available for other things than pure voli- 

 tional impulses. 



576. The preceding discussion will enable us to be very brief concern- 

 ing a question which has from time to time been much discussed, and which 

 has acquired perhaps fictitious importance, viz., the question as to how 

 volitional impulses leading to voluntary movements travel along the spinal 

 cord. The conclusions at which we have arrived, namely, that in the normal 

 carrying out of voluntary movements the chief part is played by efferent 

 impulses passing along the pyramidal tract, carries with it the answer that 

 volitional impulses travel in the spinal cord along the pyramidal tract. 



In the dog, in which the whole pyramidal tract crosses at the decussation 

 of the pyramids, we should expect to find that a break in the pyramidal 

 tract of one side of the cord at any point along its length caused loss of 

 voluntary movement on the same side below the level of the break. And 

 experiments as far as they go support this view. No one it is true has 

 attempted to divide or otherwise cause a break in the pyramidal tract alone, 

 leaving the rest of the cord intact ; and, indeed, even if an injury were 



