'2~2'2 Motor Aphasia [CHAP. 



higher speech centre ; although in close apposition and without doubt possessing associations 

 of the highest importance it does not form an integral part of Broca's area, as is clearly 

 proved by the fact that motor aphasia is not accompanied by actual paralysis of the muscles 

 concerned in articulation. For motor aphasia is definable as an annihilation of the power 

 to call into action and execute the complex associated series of oral, lingual, and laryngeal 

 movements resulting in articulate speech; it is a case of the motive power for special, 

 combined, skilled movements being in abeyance, while the muscular mechanism for simple 

 movements remains intact ; and the centre, evidently a combined one, for this higher function 

 lies apart from the several primary centres. 



Now most clinicians insist that in the lesion limited to the area of Broca, so commonly 

 productive of motor aphasia, destruction of the cortex alone is the essential factor, but this is 

 an assumption against which I must protest, and on the following grounds. 



In the first place, if an isolated patch of cortex like that covering the pars basilaris of the 

 lower frontal gyms be so specialised as regards its function it is surely reasonable to expect 

 that its structure would be likewise specialised, but to the best of my knowledge this is not 

 the case. On account of its physiological importance it is a part to which I have paid most 

 careful attention, and although its peculiar conformation renders its microscopic examination 

 in serial sections difficult, I have now been over the field so repeatedly that I think I can 

 say with safety that I have not overlooked any gross peculiarity of fibre arrangement or cell 

 lamination, and I will repeat that histologically the area of Broca pertains to the " intermediate 

 precentral " field ; its type of cortex, as displayed by the methods I have employed, does not 

 differ from that situated immediately above, nor from that extending in continuation with it 

 forwards and round to the orbital operculum ; also, so far as I am aware, no other histologist 

 has discovered any special formation in this particular cortical subdivision. 



This is of course negative evidence, but it gains in significance when all the data of 

 clinical experience, both the positive and the negative, are considered together with it. 

 Thus in cases of tumour, meningitis, and allied conditions in which the lesion though accurately 

 localised is irritative and superficial in kind, it is a matter of common knowledge that if 

 aphasia results, it is of a transient nature. On the contrary, in cases of lesion extending to 

 the underlying parts the disability is permanent. Now the condition which in the majority 

 of cases is responsible for permanent motor aphasia is the occlusion of a twig from the anterior 

 frontal branch of the middle cerebral artery specially destined for this part 1 , an occlusion 

 which may be of thrombotic or embolic origin ; and as von Monakow points out, and as I have 

 seen on careful examination of the left hemisphere of two perfect cases coming under my own 

 observation, not only is the cortex destroyed by this occlusion but the necrotic disintegration 

 penetrates deeply into the subjacent white substance placed anterior to the lenticular nuclei 

 and internal capsule, and in my opinion it there interrupts fibres of the highest importance, 

 but obviously not coming entirely from the cortex of the area of Broca, because as I have just 

 said a surface lesion limited to this area is inadequate to the production of complete and 

 permanent aphasia. 



1 The anterior frontal is usually the second branch given off by the middle cerebral artery, one to the orbital 

 lobe being the first and another to the ascending frontal gyrus the third. But the distribution of these vessels is very 

 irregular, and occasionally the twig to Broca's area is a special one, arising independently instead of from the 

 anterior frontal branch. 



