CHAP, ii.] THE BRAIN. 1063 



midal tract, and the spinal motor mechanisms remain as they 

 were before. Obviously the carrying out of a voluntary move- 

 ment 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 cortex 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 cerebrospinal 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 development 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 may be 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 learnt ; and yet, according to some definitions of 

 the word ' will ', those movements could not be said to be initiated 

 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 learnt and 

 practised by the working of an intelligent 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 suppose 

 that there has been any shifting of the machinery employed for 

 carrying 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 volitional impulses. 



663. The preceding discussion will enable us to be very 

 brief concerning a question which has from time to time been 

 much discussed, and which has acquired perhaps factitious im- 

 portance, viz. the question as to how volitional impulses leading 

 to voluntary movements travel along the spinal cord. The con- 



