82 LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



caudad to the spinal cord. Any foci of disease, therefore, which 

 are situated in the centrum semiovale must involve some of the 

 coronal fibres. They, however, do not always give rise to 

 symptoms which would lead us to suspect a break in the con- 

 ductivity from cortex to periphery. This may be because the 

 coarser and more striking lesion-symptoms, the only ones which 

 can be detected by our present means of diagnosis, require for 

 their development the destruction of the whole tract involved. 

 Apparently a small remnant of a tract suffices to conduct 

 voluntary impulses from the cortex to deeper-lying points, and 

 to convey sensory impressions from the periphery to the cortex. 



Lesions, in particular, which do not lie in the white sub- 

 stance under the central convolutions that is to say, lesions 

 which involve the tract from the cortex to the pons and the 

 tegmental radiation often give rise to no symptoms. On the 

 other hand, lesions which involve the pyramidal tracts produce 

 paralyses of the opposite half of the body. Disease of the 

 white substance under the cortex of the inferior frontal convo- 

 lution often leads to aphasia. In addition to these there are a 

 number of conditions known which make it very probable that 

 an interruption of the tegmental radiation may bring about a 

 loss of sensibility in one-half of the body. 



It is pretty well established that diseases which involve the 

 region just back of the knee of the internal capsule, diseases, at 

 least, which render the fibres incapable of conveying nervous 

 impulses, suspend the motility of the entire opposite half of the 

 body, and that lesions situated in the terminal two-thirds of the 

 posterior branch may destroy the sensation of the opposite side 

 of the body, or at least very much diminish it. In most cases the 

 sense of sight also suffers, and occasionally the sense of hearing. 

 The injury to the sense of sight takes the form of hemiopia. 



If you bear in mind that, as has been repeatedly stated, all 

 the fibres converge radially from the cortex to the capsule, you 

 will easily understand that a small lesion in the capsule may 

 give rise to the same symptoms which would be produced by a 



