1885.] on the Motor Centres of the Brain, de, 253 



it a2)i)cars to mo that in consequence of tlic rapidity with wliicli 

 function is being demonstrated to be definitely localised in various 

 l)ortions of tLe cerebral lieinisphercs, we are in danger of losing 

 siglit of Dr. Hnglilings Jackson's grand generalisations on nerve 

 function, and that we are gradually inclining to the belief that the 

 function of each part is very distinct, and therefore can most readily 

 act without disturbing another part. 



In fact, we are perhaps drifting towards the quicksands of spon- 

 taneity, and disregarding entirely the facts of every-day life which 

 show that every cycle of nerve action includes a disturbance of the 

 sensory side as well as the active motor agency. Did we in fact 

 admit the possibility of the motor corpuscle acting per se, and in the 

 absence of any sensory stimulation, we should again be placed in the 

 position of believing that an eifect could be produced in the absence 

 of a cause. 



For these reasons such a centre has been termed kinsesthetic or 

 sensori motor, and such centres exist in large quantities in the spinal 

 cord, and they perform for us the lower functions of our lives with- 

 out arousing our consciousness or only the substrata of the same. 



But now, turning to the brain, although I am extremely anxious 

 to maintain the idea just enunciated that when discussing the abstract 

 side of its functions we should remember the sensori motor arrange- 

 ment of the ideal centre, I shall have to show you directly that the 

 two sides, namely, the sensory and motor in the brain are separated 

 by a wide interval, and that in consequence we have got into the 

 habit of referring to the groups of sensory and motor corpuscles in 

 the brain as distinct centres. I trust you will not confuse these ex- 

 pressions, this unfortunately feeble terminology, and that you will 

 understand, although parts may be anatomically separated and only 

 connected by commissural threads, that functionally they are closely 

 correlated. 



In consequence of the bilateral symmetry of our bodies we possess 

 a double brain — a practically symmetrical arrangement of two in- 

 timately connected halves or hemispheres which, as you know, are 

 concerned with opposite sides of the body, for the right hemisphere 

 moves the left limbs, and vice versa. 



For my purj)ose it will be sufficient if we regard the brain as com- 

 posed of two great collections of grey matter or nerve corpuscles 

 which are connected with sensory nerve-endings, with muscles, and 

 intimately with one another. 



In this transverse section of a monkey's brain, which is stained 

 dark blue to show up its comjDonent parts, you will see all over the 

 surface a quantity of dark grey matter, which is simply the richly 

 convoluted surface of the brain cut across. Observe it is about 

 J inch deep, and from it lead downwards numerous white fibres down 

 towards the si)inal cord. The surface of the brain, the highest and 

 most complicated part of the thinking organ, is called the cortex, bark, 

 or rind, and in it are arranpred the motor centres I am about to 



