772 VOLUNTARY MOVEMENTS. [BOOK in. 



sensations derived from the several parts of the body ; we seem 

 justified in speaking of a topographical distribution of cortical 

 "sensory" areas, if we may so call them, following very closely 

 that of the motor areas ; and we know that by the numerous 

 fibres passing from the cortex to the optic thalamus, if not in 

 other ways, an anatomical path appears to be afforded for sen- 

 sory impulses. But to this point we shall return later on. 



Meanwhile we may conclude that the loss of movement which 

 follows the removal of a motor area is not due merely to the 

 loss of motor elements, it may be as much due to the loss of 

 sensory elements. Indeed it has been maintained by some that 

 the loss or impairment of movement in question is not a motor 

 business at all, but is simply due to a loss of the muscular sense. 

 We have seen, however, reasons for thinking that the pyramidal 

 tract is certainly an efferent tract, and injury to it in its begin- 

 ning in the cortex must lead to failure of efferent impulses. 

 Moreover, though removal of the cortex does appear to interfere 

 with muscular sense, it also, and even more clearly, interferes 

 with cutaneous and other sensations. The conclusion which 

 we ought to draw from the above facts is perhaps rather this, 

 that the relations of the cerebral cortex are manifold, and that 

 the carrying out even of a simple voluntary movement is a very 

 complicated matter ; even if we assume that the cell in the cor- 

 tex giving origin to a fibre of the pyramidal tract is in nature a 

 motor cell, we must also recognize that its work is determined 

 by ties which bind it to other elements of the cortex and through 

 them to other parts of the nervous system and indeed of the 

 body. The connections of a sensory nature between a motor 

 area and the part to whose movements it is related is strikingly 

 shewn by results which may make their appearance when stimu- 

 lation of the cortex is carried on 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 move- 

 ment. 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 fol- 

 low 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 con- 



