170 CEREBRAL LOCALIZATION 



third frontal gyms, but rather to look to the temporal 

 region, especially if there is any defective appreciation 

 of what is said or written. Moreover, we receive 

 encouragement that there is no need to fear that 

 small cortical injuries inflicted by the surgeon will 

 cause aphasia ; subcortical injuries are much more 

 likely to do so, by cutting off projection fibres. 



MISLEADING LOCALIZING SIGNS OF INTRA- 

 CRANIAL TUMOUR. 



It is very disappointing when definite signs usually 

 regarded as of importance in localization give colour 

 to a diagnosis as to the position of a cerebral tumour, 

 but on the operation table nothing is found in that 

 region. It is more than disappointing, because un- 

 successful attempts to find the tumour are more fatal 

 than actual removals. Some study therefore of the 

 physiology of the production of misleading signs may 

 be useful. 



The principal traps are furnished by the following : 



i. CRANIAL NERVE PALSIES. Paralysis of one or 

 both sixth cranial nerves is quite common, and by 

 no means proves that the nerve itself or its nucleus 

 is involved in the lesion. It has been accounted for 

 by stretching, due to a supposed backward dis- 

 placement of the whole brain late in the development 

 of a growth ; the abducent nerves run straight 

 forwards and are slender, so the first sign of the 

 displacement is a convergent squint. 



Other cranial nerves, including the third, fifth, 

 seventh, and eighth, are occasionally affected by dis- 

 placements of the brain or by pressure. 



