Motor Area tj r 



ing parietal convolutions. The wrist and ringers have their centres in 

 the middle of the ascending parietal convolution, and the lowest of 

 them is close against the centre for the mouth and face. Watch a 

 man trying his very hardest to tie, or to untie a knotted cord, and 

 note how the muscles of the corner of his mouth and of his face are 

 at work. The vigorous motor impulse generated in the hand-centre is 

 brimming over and stimulating the neighbouring oro-facial centre. 

 Suppose that during this effort the branch of the middle cerebral 

 artery which supplies the hand-centre were to burst, there would at first 

 be a meaningless twitching of the hand and mouth, and, as the blood- 

 clot grew, the centres would become disorganised, and the man might 

 be left with brachio-facial paralysis on the opposite side to the injury, 

 of course (p. 49). And thus it comes about that brachio-facial paralysis 

 is of more common occurrence than brachial monoplegia or facial 

 monoplegia. There is no anatomical boundary between the arm- 

 centre and the centres adjacent to it. In cerebral paralysis there will 

 be neither loss of consciousness nor sensation if only the motor area 

 be implicated. 



Again, watch the demagogue upon the rostrum. The louder he 

 speaks, the more he throws his arm about, because the energy in his 

 speech-centre flows into the neighbouring hand-and-arm-centre. And, 

 as the speech- centre is upon the left hemisphere, it is the right arm 

 with which he gesticulates ; it is training only which makes the orator 

 use his left arm to vary the monotony of the brachial movement. I 

 do not know if the man whose speech -centre is upon his right side in 

 his oratory neglects the use of his right hand, but I expect that he does, 

 unless, indeed, he be a well-trained speaker. 



Some untrained speakers, or ranters, throw out both arms in an 

 emphatic manner ; this is because the centres of the two sides are 

 held in association by certain commissural fibres. The need for such 

 fibres is evident ; were there none of that sort, the facial muscles of 

 one side, for instance, would be able to act without regard to those of 

 the other, expression being reduced to an absurdity. In very many 

 of our common acts, such as eating, talking, breathing, walking, it is 

 essential that the muscles on the two sides of the body be in harmonious 

 association, and the existence of commissural fibres by which this is 

 effected must not be overlooked when problems in paralysis are being 

 worked out. 



Facial monoplegia is rare ; facial paralysis of cerebral origin usually 

 being associated with brachial paraplegia when the lesion spreads 

 upwards, or with aphasia when it implicates the base of the third 

 left frontal convolution. 



The oro-lingual centres (which are at the lower end of the fissure of 

 Rolando) of one hemisphere are associated in their work with those 

 of the other side by certain cross-fibres ; for, as already suggested, 

 one does not use a lateral half of the tongue separately, nor does one 



