CAPSTJLA INTEENA, CORPUS STRIATUM, INTERBRAIN-GANGLIA. 253 



central convolutions — that is to say, leaions which involve the cortical tracts to the 

 pons and the tegmental radiation — often fail to give rise to symptoms. Focal lesions, 

 on the other hand, that involve the pyramidal tract produce paralysis of the opposite 

 half of the body. Disease of the medullary substance under the cortex of the in- 

 ferior frontal convolution often leads to aphasia. Moreover, cases are known which 

 make it extremely probable that interruption of the tegmental radiation may lead to 

 a unilateral loss of sensibility. Two cases recently observed by the author show that 

 the pains which appear after apoplexies may at times be explained through the prox- 

 imity of the lesion and the tegmental radiation. 



It appears fairly-well established that diseases which involve the region poste- 

 rior to the knee of the internal capsule — that is, diseases which make the fibers 

 running in this region incapable of conduction — suspend the motility of the entire 

 opposite half of the body; that lesions situated in the terminal two-thirds of the 

 posterior limb destroy the sensibility of the opposite halt of the body, or at least 

 diminish it very much. In most cases the sense of sight suffers also, and probably 

 hearing at times. The disturbance of sight appears In the form of hemiopia. 



Cortical centers for leg, for arm, for face. 



Centrum semioTale 



Cupsula interna 



Fig. 164. 



If you bear in mind what has been repeatedly stated: that all the fibers con- 

 verge from the cortex toward the internal capsule, it will be easily understood that 

 small lesions in the internal capsule may produce the same symptoms as larger ones 

 in the centrum semiovale, or still more extensive lesions in the cortex. In the internal 

 capsule fibers lie close together which higher up are spread out over a greater space. 

 For example, a very extensive cortical territory (one including both central con- 

 volutions and the parts of the frontal and parietal convolutions closely bordering on 

 them ) must be destroyed if complete crossed hemiplegia is to be produced. A smaller 

 lesion in the medullary substance of the centrum semiovale under the central gyri 

 might have the same effect. In the internal capsule, on the other hand, the destruc- 

 tion of a small portion alone of the posterior limb suffices to call forth the combina- 

 tion of symptoms. In cases of hemiplegia, therefore, we will always think, first of 

 all, of lesions which are in the neighborhood of the internal capsule or are situated 

 in it, if additional symptoms do not point directly to other regions of the brain. 



