ON VOLUNTARY MOVEMENTS. 679 



573. We may now return to the discussion of the question, What is 

 the part played by a motor area, and by the contribution 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 con- 

 clusion 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. It is perfectly true that in many cases at least the removal of a 

 cortical area has led to diminished sensibility of the part in which move- 

 ments are excited by stimulation of the area ; and there are many facts, of 

 which we shall presently quote a very striking one, which go to show that 

 the cortex of the motor region is largely influenced by sensory impulses from 

 various parts of the body ; but we cannot suppose that the pyramidal tract 

 is the channel by which such sensory impulses reach the cortex. As we 

 have previously ( 481) urged, the fact that the degeneration of the fibres 

 in the tract is a descending one, and cannot be trusted by itself to prove 

 that the direction in which the fibres carry impulses is only that from the 

 cortex downward ; but this added to 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, leaves no doubt 

 that the tract is one of efferent fibres. Hence we may infer that whatever 

 be the nature of the events taking place in a motor area during the carry- 

 ing 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 con- 

 cerned. 



Let us consider first the movements of speech in man, the evidence touch- 

 ing 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 certainly say of it that it has to be" learned." 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 

 character ; if we are at all able to gather the wish of the speaker, we recog- 

 nize that he is attempting to utter the right words in the right sequence, but 

 that his efforts are frustrated by imperfect coordination or imperfect mus- 

 cular action ; his speech is " thick," the syllables are blurred and the like. 

 Disease of the bulb at times leads to imperfect speech of this kind in which 

 the imperfection may be recognized as due to the lack of proper coordina- 

 tion of motor impulses. The affection of speech known as "aphasia," 

 which is caused by lesions of the cortex, is of a different character, and the 

 forms of imperfect speech caused by bulbar disease have justly been distin- 

 guished from true aphasia by the use of other terms. Cases of complete 

 aphasia in which all power of speech is lost, do little more than help us to 

 ascertain the topographical position in the cortex of the " speech " area, but 

 cases of partial aphasia are especially instructive. Without attempting to 

 go into the details of the subject and into the many considerations which 



