448 ZOOLOGY FOR MEDICAL STUDENTS chap, xiii 



activities of the mammal. This is shown in the case of man by the fact 

 that the faculty of language, which is simply a particular aspect of thought, 

 is located in definite regions of the cortex. The study of localized injury 

 of the cortex through accident or disease has brought out the fact that 

 a particular part of the auditory region is responsible for dealing with 

 thought expressed in spoken words, and a part of the visual area 

 with thought expressed in written or printed characters ; while on 

 the other hand definite motor areas are charged with the conversion of 

 thought in the other direction into in the one case spoken language and 

 in the other written. 



Along with the specialization of various regions of the cortex in relation 

 to special functions there has taken place pari passu a higher and higher 

 perfection of nervous connexion between the various parts so that they 

 remain linked together in the most intimate way as a functional whole. 

 Thus the various parts of the hemisphere are linked together by 

 countless association fibres : they are also linked with other subsidiary 

 centres in the brain or spinal cord of whose activities they have assumed 

 control : and they are linked up with their fellows on the opposite side 

 of the brain by elaborate transverse commissures such as the immense 

 corpus callosum which links together the neopallium of one hemisphere 

 with that of the other. 



