74Q 



THE CEREBRAL CORTEX. 



excitation of the frontal (and of the occipital) cortex produces conjugate 

 movements of both eyes towards the opposite side, i.e. from left towards right. 

 Similarly by an appropriate experiment, the internal rectus can also be 

 inhibited after section of the sixth nerve, so as to produce an outward move- 

 ment of the globe. Inhibition of the tonus of the antagonistically acting eye 

 muscles can thus be elicited from the cortex. The same may occur volitionally. 

 The action does not take place necessarily through the opposite cortex, for it 

 will occur if the area on the opposite side be removed, nor does it occur 

 through the occipital area when the frontal is stimulated. And vice versa, 

 on stimulation of the occipital area it does not occur through the frontal 

 area, for these two areas can be severed from one another by a vertical 

 incision through the brain, and the inhibition is still found to take place. 

 The action is therefore directly on the lower centres. This is known also to 

 be the case with the contraction effects, 1 so that it would appear that the 

 inhibitory phenomena follow the same paths as the excitatory. 



Equal and simultaneous excitation of two similar points in the focal 

 part of this frontal area in both hemispheres produces visual fixation, 

 with the eyes either in the primary position or slightly convergent. If 

 the electrodes are placed on the upper part of the area, the movement 

 may be simply downwards ; if on the lower part, simply upwards. 2 A 

 similar convergence is got, even if both right and left third and fourth 

 nerves are previously divided. 3 This effect must be due to inhibition 

 of the tonus of both external rectus muscles. 



In rare instances stimulation of the area on one side causes move- 

 ments of the head and eyes to the same side, even if none of the nerves 

 are severed. This may be due to the stimulus to inhibition being, 

 under the immediate conditions of the experiment, more effectual than 

 that to contraction. 



Eemoval of the area on one side of the brain causes the head and 

 eyes to be turned towards the side of the lesion, due doubtless to 

 muscular paralysis. The effect passes off after a day or two, a statement 

 which also applies to other bilateral movements. Nor is there any 

 obvious permanent paralysis, even on removing the area on both sides. 

 This is not to be wondered at, considering that movements of the 

 head and eyes are elicited from other considerable areas of the cortex 

 (occipital, temporal). 4 



2. The area connected with movements of the face, mouth, 

 throat, and larynx.— This area embraces rather less than the lower 

 half of the two central convolutions (Fig. 336). It is bounded above by 

 a line joining the angle of the precentral sulcus with the lower end of 

 the intraparietal sulcus, and extends below to the Sylvian fissure. 5 



1 Schafer, Brain, London, 18S8, vol. xi. ; Mott and Schafer, ibid., vol. xiii. p. 169. 



2 In Cercopifhcciis, Mott and Schafer, loc. tit., p. 170. 

 s Sherrington, loc. tit. 



4 Extirpation in the dog of the centre for movements of the ocular muscles (7 in Fig. 332), 

 also does not appear to have any permanent effect upon those movements. See Eckhard, 

 Oentralbl. f. Physiol., Leipzig u. Wien, 1898, No. 1 ; R. du Bois-Reymond and P. Silex, 

 Arch. f. Physiol. , Leipzig. 1 899, S. 174. This last paper also contains an account of observa- 

 tions on the effects of excitation of the centre in the dog (see also on this subject, 

 v. Bechterew, Arch. f. Physiol., Leipzig, 1899, S. 500). The extensive paralytic pheno- 

 mena described by Grosglick as resulting from ablation of the frontal lobes {Arch. f. 

 Physiol., Leipzig, 1895, S. 98), are probably due to an implication of other regions in the 

 lesion. 



5 Beevor and Horsley described {Phil. Trans., London, 1887, B, Plate vii., Figs. 7 and 

 8) primary movements of the thumb over the upper two-thirds of this area, but there 

 must have been some unrecognised source of error in this observation. 



