186 CLINICAL APPLIED ANATOMY. 



where a connection is established with the third nerve, i.e., the 

 lesion producing the hemianopia must be above the external 

 geniculate body, and somewhere between it and the occipital 

 cortex. 



Hearing may be involved as the result of tumour pressure on 

 the auditory nerve. Tumours in the pons or at the base of the 

 brain can do this, and the deafness is on the same side as the 

 lesion. Tumours of the auditory centre in the temporo-sphenoidal 

 lobe may also produce subjective noises or deafness and then the 

 deafness is of the opposite ear owing to the decussation of the 

 tract. 



Intracranial tumours which spring from the base of the skull 

 are usually either sarcomatous or carcinomatous. Their usual 

 seats are the petrous portion of the temporal bone, the sella 

 turcica or the occipital bone in the neighbourhood of the foramen 

 magnum. Growths in the region of the sella turcica tend to 

 compress all the nerves of one eyeball and may press on the 

 optic chiasma with results already mentioned ; they may also 

 cause loss of smell by pressure on the olfactory tract. Growths 

 of the petrous bone are adjacent to the Gasserian ganglion and 

 the fifth nerve, hence they may produce facial neuralgia, 

 anaesthesia in the territory of the fifth nerve, paralysis of 

 masticatory muscles, and even keratitis. These tumours may 

 also invade the posterior fossa, since the petrous bone is one of 

 its boundaries. The nerves of the posterior fossa may thus be 

 involved and occlusion of the lateral sinus also result. In the 

 substance of the petrous bone the growth may erode the carotid, 

 and so produce bleeding from the ear, whilst masses of glands 

 may appear beneath the mastoid deep in the upper part of the 

 neck. Tumours in the neighbourhood of the foramen magnum 

 may implicate any of the nerves behind the fifth, but chiefly the 

 lower ones. They also exercise pressure on the motor tract for 

 the opposite side of the body, but cannot produce conjugate 

 deviation of the eyes, since for this to occur the nucleus of the 

 sixth nerve within the pons must be involved. 



Tumours of the middle and anterior fossae of the skull may 



