284 CEREBRAL LOCALIZATION 



Broca's convolution for uttering speech is uncertain^ 

 but probably there is. Lesions of the projection 

 fibres from the cortex ( (?) of Broca's convolution) 

 will cause " anarthria," that is, loss of external but 

 not of internal speech. 



Practical deductions are not to trust aphasia as 

 conclusive localizing evidence of a lesion in the left 

 third frontal gyrus, but rather to look to the temporal 

 region, especially if there is any defective appreciation 

 of what is said or written. Patients with left tem- 

 poro-sphenoidal abscess, for instance, are usually 

 unable to name correctly objects shown them. More- 

 over, 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 



