84 LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



closely crowded together that a focus of disease could scarcely 

 involve individual fibres without affecting others. Disease of 

 the cortex, however, not infrequently causes monoplegias and 

 monospasms. In this portion of the brain a relatively large 

 area may be involved without impinging on an adjoining centre. 

 The accompanying diagram will effectually impress these state- 

 ments upon your mind. It shows why monoplegias most 

 frequently have a cortical origin, whereas hemiplegias generally 

 result from disease of the deeper-lying portions of the brain. 

 We see at a glance that a lesion of a given extent, situated in 

 the cortex, may easily affect only one centre, whereas the same 

 focus, more deeply situated, might affect the radiating fibres of 

 many centres. 



We have not yet learned what symptoms would arise from 

 involvement of the association-fibres alone, because these fibres 

 are so closely blended with those of the corona radiata. Pos- 

 sibly certain forms of disturbance in speaking, reading, and 

 hearing belong in this category. We know, too, very little con- 

 cerning the symptoms arising from destruction of the corpus 

 callosum. It appears that this may, under certain circumstances, 

 be entirely destroyed without giving rise to disturbances of 

 motility, of co-ordination, of sensibility, of the reflexes, or of 

 the special senses, and without any material disturbance of the 

 intellect. One case of disease of the corpus callosum has been 

 observed accompanied by an uncertain gait, but without vertigo 

 or ataxia. 



