62 Precentral or Motor Area [CHAP. 



Instances of lesions which have been so limited in their effects as to produce paralysis 

 of the trunk muscles only, are not quoted by any of the authorities I have consulted, and 

 there is no clinical evidence to show whether or not the centre for the control of these 

 muscles lies, as I have already suggested, at the level of the annectant Rolandic gyms. 



But that the arm centre lies below the level of this gyrus there is abundant proof. 

 The majority of the reported cases of brachial monoplegia have been the result of occlusion 

 of twigs of the ascending frontal branch of the middle cerebral artery, though some excellent 

 cases have followed injuries of the parietal bone, and the area accepted by clinicians as the 

 arm centre occupies the middle two-fourths of the Rolandic cortex. 



An isolated cortical facial paralysis seems to be extremely uncommon, but a facio-brachial 

 or a facio-lingual palsy is frequent, and a lesion of the inferior fourth of the central con- 

 volutions along with the opercular portions of the third frontal convolution is described as 

 equivalent to its production. Of course when such a lesion occurs in the left hemisphere it 

 is associated with motor aphasia. 



To put the matter briefly, we have the satisfaction of knowing that the facts derived 

 from these sources, an investigation of clinical cases, an examination of the special patho- 

 logical material which I have dealt with, and experimental research are all in harmony in 

 regard to the sequence of motor representation on the cortical surface. 



There are other points of interest having a bearing on the motor function, such as the 

 question of restitution of function after destruction of a part of the motor cortex ; the 

 difference in the results attending lesions of the cortex and of the motor tract in its intra- 

 cerebral course ; the various degenerations following such lesions ; the pathogenesis of spasmodic 

 muscular affections, etc., but these questions do not come within my province and so far as 

 localisation is concerned little is to be gained by discussing them. The more important 

 question of the localisation of skilled movements will be considered in the chapter on the 

 " intermediate precentral " area. 



Points in the Development of the Motor Cortex. 



It seems that a study of the developing cortex affords little information on the question 

 of the difference in function between the precentral and postcentral gyri. If our view on 

 the limitation of the motor function to the precentral gyrus be correct, we would expect, 

 in accordance with what we know of the tardy development of the motor tract in the spinal 

 cord, that the myelinisation of the cortex of that convolution would be deferred in a cor- 

 responding manner. But on this point the evidence is contradictory, for while Vogt figures 

 and describes a special band of fibres proceeding to the postcentral gyrus, which he says 

 is medullated in advance of others in this region, Flechsig, even in his most recent paper 

 (March 1903), mentions no difference as regards the period of maturation of the fibres of 

 the two central gyri, stating merely that the fibres of both, with the exception of fibres in 

 the olfactory regions, are the first in the whole cerebral cortex to acquire a medullated sheath. 

 In course of time, however, Flechsig may modify his views on this point 1 . 



1 In a paper by Hiisel, which has appeared since this was written, it is stated that the first medullated fibres 

 received by the central gyri come from the ventral nucleus of the optic thalaraus (fibres of the Ruban de Reil). 



