MOTOR CENTRES IN MAN. 699 



in man, exist in part on the convolutions bounding the fissure of Rolando, and 

 occupy the "central" convolutions, i.e., the ascending frontal and ascending 

 parietal convolutions along with the superior parietal lobule, and along the mesial 

 surface of the hemisphere, the paracentral lobule and precuneus (fig. 488). In this 

 region, the upper third of the ascending frontal and parietal convolutions along 

 with the superior parietal are the leg area (fig. 488, leg), the middle third of the 

 ascending parietal and ascending frontal for the arm, and the upper part of the 

 lowest third of these convolutions for the face, while the very lowest part of the 

 ascending frontal convolution is the area for the movements of the lips (L) and 

 tongue (T). (Compare figs. 485, 490.) The last area, with the posterior extremity 

 of the third left frontal convolution, is the centre for voluntary speech. We can- 

 not say whether these " centres " are sharply mapped off from each other. In any 

 case a very strong stimulation of one centre may involve an adjacent area. So far 

 as is yet known, centres Nos. 5 and 12, as represented on the monkey's brain 

 those on the posterior extremity of the superior and middle frontal convolutions, 

 (5) for extension forward of the arm and hand, and (12) for opening the eyes and 

 turning the head towards the opposite side (as in surprise), are not represented in 

 the human brain. So accurately have certain of these areas been located, that 

 surgeons, in suitable cases, have been able to excise a tumour causing certain 

 symptoms, with relief of those symptoms.] 



[We may, therefore, assert as a general proposition that the muscles of one 

 lateral half of the body are regulated by certain areas in the opposite cerebral 

 hemisphere.] 



[Gowers maintains that the motor region is not exclusively motor, but that destruction of this 

 area also leads to some loss of sensation. Starr also asserts that perceptions occur in the grey 

 matter of the cortex of the "central" region'and parietal convolutions, and that the various sensory 

 areas for the various parts of the body lie about, and coincide to some extent with, the motor 

 various areas for similar parts, but the sensory area is more extensive than the motor area, 

 extending into the parietal behind the motor area, which is confined to the ascending frontal 

 and parietal convolutions.] 



II. Method of Destruction or Ablation of Parts of the Cortex. Much confusion in this 

 matter has arisen from comparing the results obtained on animals of different species. [It seems 

 quite certain that the results obtained in the dog are quite different from those in the monkey. 

 The motor areas may be simply excised with a knife, or the surface of the brain may be washed 

 away with a stream of water, as was done by Goltz in dogs.] 



. [In the dog, the areas which are described as motor may be removed either by the knife 

 {Hermann) or by means of a stream of water so directed as to wash away the grey matter 

 (Goltz). In both cases, although there was some paralysis on the opposite side of the body, 

 this was but temporary, for the paralysis disappeared within a few days, the animals having 

 very decided control over their muscles, although Goltz admits that certain acts, especially 

 those which the dogs had been trained to execute, e.g., giving a paw, were executed " clumsily," 

 indicating some failure of complete control, which Goltz ascribed to loss of tactile sensibility. 

 Goltz thinks that the extent of the injury has more to do with the result than the locality. 

 The restoration of motion was not due to the action of the corresponding centre of the opposite 

 side, as destruction of this centre, although it produced the usual symptoms on the side which 

 it governed, had no effect on the previous result (Carville and Duret).] 



[In the monkey, there can be no doubt from the experiments of Ferrier that 

 destruction of a motor centre, e.g., that for the arm, results in permanent paralysis 

 of the arm of the opposite side, and if the centres for the arm and leg are destroyed, 

 there is permanent hemiplegia of the opposite side. " In order that the hemiplegia 

 or paraplegia produced by cortical ablation shall be complete, it is necessary to 

 include the part of the marginal gyrus corresponding in longitudinal extent to the 

 excitable areas of the external surface." The amount of paralysis produced by 

 ablation of the marginal gyri alone is as great as that caused by removal of the 

 much more extensive external areas ; but the complexity of the muscular move- 

 ments which are governed from these areas is much greater than in those governed 

 from the marginal gyrus (Schafer and Horsley).'] 



