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CHAPTER XL 

 CEREBRAL LOCALIZATION. 



The causation and significance of optic neuritis. Localization 

 in the cerebellum. Tumours in the cerebello-pontine angle. 

 Localization of sensation in the cerebral cortex. Functions of 

 the frontal cortex. Spasticity. Apraxia. Aphasia. Misleading 

 localizing signs of cerebral tumour. The cerebrospinal fluid. 



IT will be necessary here to assume that the reader 

 has an ordinary acquaintance with the structure 

 and functions of the brain. We shall confine our- 

 selves to a brief reference to the most important 

 advances of the past decade in providing evidence 

 for the localization of tumours, abscesses, and 

 traumatic lesions, and therefore for their successful 

 treatment by operation. 



OPTIC NEURITIS. 



It has long been in doubt why optic neuritis should 

 develop in cases of cerebral tumour. It has been 

 attributed to the effects of chronic meningitis, and 

 to over-filling of the third ventricle, with consequent 

 pressure on the underlying optic chiasma. It is 

 now definitely established by the experiments of 

 Gushing and Bordley, and confirmed by clinical 

 experience, that it is a pressure effect. The growth 

 of the neoplasm causes a great and continued rise 

 of intracranial pressure ; this tends to dam back 

 the lymph flow returning in the sheath of the optic 

 nerve. The usual consequence of lymphatic obstruc- 



