1885.] on the Motor Centres of the Brain, the. 257 



haemorrhage has ploughed up the interior of the brain. Here is tlie 

 cortical grey matter, but its fibres leading down to the muscles are all 

 destroyed. 



Now in examining this patient I asked him to move his left arm 

 or leg ; he was perfectly conscious, and understanding the question, 

 made the effort as we say, but no movement occurred. 



Now if both sides of the body are represented in each hemisphere, 

 it seems to me that such a case would be impossible, or at least that 

 a little practice would enable the other hemisphere to do the work ; 

 but all clinical facts say that, once destroyed, the loss is never 

 recovered. 



If we examine this motor region of the cortex with the microscope, 

 we of course find these large corpuscles, which we have learnt are 

 those which alone give energy to the muscles. 



But you must not imagine that the motor region consists solely of 

 these corpuscles. On the contrary, as you see in this diagram, we 

 have several layers of corpuscles. I shall return to this arrangement 

 of the corpuscles directly. 



Looking back at the surface of the brain, you notice that I have 

 only accounted for but a small portion of the cortex. Dr. Ferrier 

 was the first to show that the portion of cortex which perceived (and 

 I use the word in its strictest sense) the sensation of light was this 

 part, and it is therefore called the visual centre or area. From 

 recent researches it would appear that we must give it the limits 

 drawn on this diagram. Below it we find the centre for hearing. 



Thus we know where two sense percej^tive centres are situated. 



Microscopical investigation shows that this sensorial portion of 

 the cortex is very deficient in large corpuscles, and is correspondingly 

 rich in small cells. Here in this diagram you see these two kinds 

 of structure in the cortex cerebri. Note the greater number and 

 complication of the small corpuscles in the sensory part of the cortex, 

 and the comparatively fewer though much larger corpuscles in the 

 motor region. 



It seems to me that several beliefs are justified by these facts. 



In the first place, the movements produced by the action of these 

 motor centres are always the same for the same centre; consequently 

 it has only one thing to do, one idea as it were. Thus, for instance, 

 bending of the arm ; this action can only vary in degree, for the elbow 

 will not permit of other movements. Hence we may look upon it as 

 one idea. Now observe that where one idea is involved, we have but 

 few corpuscles. 



Next consider the multitude of ideas that crowd into our mind 

 when we receive a sensation. One idea then rapidly calls up another, 

 and so we find anatomically that there are a corres^Donding much 

 greater number and complication of nerve corpuscles. 



To sum up, I believe we are justified in asserting that where in 

 the nervous system a considerable intensity of nerve energy is re- 

 quired (e. g. for the contraction of muscles) you find a few large cor- 



VoL. XI. (No. 79.) s 



