INTKACRANIAL TUMOUES. 181 



is usually in the outer and fore part of the hemisphere, the 

 dentate nucleus and its fibres escape and paralysis of the above 

 type is then absent. Cerebellar lesions do not produce any 

 anaesthesia. 



Barely the abscess lies in the flocculus and then the cranial 

 nerves in the proximity may be paralysed. The nerves in im- 

 mediate relation are the seventh, the eighth and the pars 

 intermedia; but the fifth, sixth, ninth and tenth are not far 

 off. Unfortunately for localisation, the seventh and eighth 

 nerves may be affected in the diseased petrous bone and 

 indeed are more likely to suffer here than in the neighbour- 

 hood of the flocculus. 



INTRACRANIAL TUMOURS. 



After obliteration of the fontanelles, a process which is com- 

 plete before the second year of life, the cranium is practically a 

 closed cavity. The majority of intracranial tumours occur some 

 time after this closure, i.e., between puberty and middle adult life, 

 hence the pressure effects produced by these growths are more 

 marked and more extensive than those produced by new growths 

 in any other part, save perhaps the vertebral canal. Tumours 

 growing in the thorax and bony pelvis afford the nearest approach 

 to similar conditions elsewhere in the body. Tuberculous tumours 

 sometimes occur before the period of closure of the anterior fon- 

 tanelle, but even then the mass often lies below the tentorium 

 cerebelli, and so the patency of this fontanelle has but little 

 modifying influence on the direct pressure symptoms, although 

 it may permit distension of the ventricles of the brain. 



The strength and firm attachment of the tentorium cerebelli, 

 which forms a fibrous dome over the posterior fossa of the skull, 

 account for the marked pressure symptoms associated with 

 tumours which grow beneath it. The parts of the brain which 

 lie in the posterior fossa are the cerebellum, medulla, pons, and 

 cranial nerves below the fifth. The veins of Galen and the 

 straight sinus may be occluded by subtentorial tumours, and 



