CHAP, ii.] THE BRAIN. 769 



which a first aphasia, due to a lesion on the left side, has been 

 followed by a second aphasia due to a sequent lesion occurring 

 on the right side. On the whole perhaps the evidence of clini- 

 cal study tends to shew that in man the loss of movement due 

 to the destruction by disease of an area is a permanent one, 

 though actual demonstration of this is wanting. 



489. We may now return to the discussion of the ques- 

 tion, what is the part played by a motor area, and by the con- 

 tribution from that area to the pyramidal tract in carrying out 

 the movements with which the area is associated? 



We may premise that the evidence points very distinctly to 

 the conclusion that whatever be the nature of the whole chain of 

 events of which the cortical area seems to be a sort of centre, 

 the fibres of the pyramidal tract serve as the channel of processes 

 which we must regard as efferent in nature. The characters of 

 the fibres, axis cylinder processes terminating, so far as we can 

 ascertain, in connection with motor cells, the fact that the degen- 

 eration of the fibres is a descending one, though this cannot be 

 trusted by itself to prove that the direction in which the fibres 

 carry impulses is only that from the cortex downwards, and above 

 all the fact that when the fibres of the tract are stimulated at 

 any part of their course, movements, the signs of the occurrence 

 of efferent centrifugal impulses, are produced, these things 

 together, leave no doubt as to the tract being one of efferent 

 fibres. Hence we may infer that whatever be the nature of the 

 events taking place in a motor area during the carrying out of 

 a movement, the part played by the fibres of the pyramidal tract 

 is that of carrying efferent impulses from the area to the muscles 

 concerned. N 



Let us consider first the movements of speech in man, the 

 evidence touching the connection of which with an area on the 

 third frontal convolution appears so very clear. Speech is 

 eminently a 'skilled' movement; it involves the most delicate 

 coordination of several muscular contractions, and we may cer- 

 tainly say of it that it has to be * learnt.' The whole chain of 

 coordinated events by which the utterance of a sentence, a word, 

 or any vocal sign is accomplished consists of many links, the 

 breaking of any of which will lead to failure of one kind or 

 another in the act. Something may go wrong in the glossal or 

 other muscles, in the nerve endings in those muscles, or in the 

 fibres of the nerves, hypoglossal and others, between the central 

 nervous system and the muscles, or something may go wrong in 

 that part of the central nervous system, the bulb to wit, in which 

 a certain amount of coordination is carried out just previous to 

 the issue of the motor impulses. Damage done to any of these 

 parts of the mechanism may lead to dumbness or to imperfect 

 speech. In the latter case the imperfections have a certain char- 

 acter ; if we are at all able to gather the wish of the speaker, 



49 



