1060 VOLUNTARY MOVEMENTS. [BOOK IIL 



half of the hemisphere and indeed is not any part at all of the 

 whole pyramidal system. The ' will/ whatever be the processes by 

 which it takes origin, and wherever be the place where they are 

 carried on, is able in the absence of the pyramidal system to 

 produce its effect on the motor fibres of the brachial nerves by 

 working on other parts of the central nervous system. 



Hence while admitting as we must do that in the intact animal 

 the cortical area and pyramidal tract play their part in carrying out 

 voluntary movements, their action is not of that simple character 

 supposed by the view referred to above. On the contrary, we are 

 driven to regard them rather as links, important links it is true, 

 but still links, in a complex chain. As we have already urged, we 

 may probably speak of the changes taking place in the pyramidal 

 fibres as being on the whole of the nature of efferent impulses ; 

 but we should be going beyond the evidence if we concluded that 

 they were identical with the ordinary efferent impulses of motor 

 nerves. And above all it must not be left unnoticed that the cortical 

 area has close if not direct connections of a sensory nature with the 

 part in whose movements it is concerned. This is shewn by the 

 following remarkable results which may make their appearance 

 when stimulation of the cortex is carried while the animal (dog) is 

 in a particular stage of the influence of morphia. If a subminimal 

 stimulus be found, that is a current of such intensity that applied 

 to a motor area it will produce no movement, but if increased ever 

 so slightly will give a feeble contraction of the appropriate muscles, 

 it may be observed that a slight stimulus, such as gently stroking 

 the skin over the muscles in question, will render the previous 

 subminimal stimulus effective and so call forth a movement. 

 Thus if the area experimented on be that connected with the 

 lifting of the forepaw, and the subminimal stimulus be applied 

 to the area at intervals, after several applications followed by no- 

 movements, a gentle stroke or two over the skin of the paw will 

 lead to the paw being lifted the next time the stimulus is applied 

 to the area. A similar result, but less sure and striking, may 

 follow upon the stimulation of parts of the body other than the 

 part corresponding to the area stimulated. Then again it has 

 been observed that in certain other stages of the influence of 

 morphia, the cortex and the rest of the nervous system are in 

 such a condition that the application of even a momentary 

 stimulus to an area leads not to a simple movement but to a long- 

 continued tonic contraction of the appropriate muscles. Under 

 these circumstances, a gentle stimulus, such as stroking the skin, 

 or blowing on the face, applied immediately after the application 

 of the electric stimulus to the area, suddenly cuts short the 

 contraction, and brings the muscles at once to rest and normal 

 flaccidity. 



These experiments shew that the development of the processes 

 in the cortex leading to the issue of what we have agreed to call 



