(_E_) =To the occipital lobe.= _Headache_ may be localized to the back of the head, and _optic neuritis_ is usually both early in onset and intense in degree. Perhaps the most important localizing symptom is _homonymous hemianopia_--blindness in the temporal half of the retina on the same side as the lesion and in the nasal half of the opposite eye. This is explained by the fact that the fibres of the optic radiation, passing forwards from the affected occipital region, supply those retinal areas. The reaction of the pupil will be unaltered, for the pupillary nerve-fibres, in their course towards the third nerve nucleus, are only directed backwards as far as the anterior corpora quadrigemina. Consequently, an interruption of optic fibres between retina and third nerve nucleus brings about a loss of pupillary reflex when light is thrown on the blind portion of the retina, whilst if the lesion be situated further back, pupillary reaction is unaltered. This is Wernicke’s sign. (_F_) =To the subtentorial region.= Certain symptoms are more or less common to all subtentorial tumours, whether they arise within the cerebellar substance (intra-cerebellar) or immediately outside the brain-substance (extra-cerebellar). _Headache_ is very severe, and in about 50 per cent. cases, localized to the back of the head, perhaps associated with stiffness of the neck muscles and retraction of the head. _Optic neuritis_ is early in onset and intense in degree. It is more constant in cerebellar tumour formation than in tumours located in almost any other part of the brain. The choking of the disk is marked and hæmorrhages are frequent. _Vomiting_ and other symptoms referable to increased subtentorial pressure--slow pulse, altered rhythm of respiration, &c.--are usually well marked. [Illustration: FIG. 69. THE VISUAL PATHS. O.L., Occipital lobe; O.R., Optic radiation; O.T., Optic tracts; P., Pupillary fibres from optic tract to third nerve nucleus; O.C., Optic chiasma; O.N., Optic nerve; 1, Blindness of affected eye; 2, Bitemporal hemianopia; 3, Bilateral homonymous hemianopia, with hemianopic pupillary reaction; 4, Bilateral homonymous hemianopia, pupillary reaction normal.] _Vertigo_ is most apparent when the patient is suddenly changed in position or tries to stand or walk. It appears in two forms, either as a definite sense of movement of self (subjective vertigo) or of objects (objective vertigo), or merely as a giddy feeling. In objective vertigo the sense of displacement of objects is more commonly from the side of the tumour towards the sound side. Vertigo is dependent on the influences exercised by the tumour on the cerebello-vestibular apparatus, and on irritation of those branches of the fifth nerve which are distributed to the dura mater in the immediate neighbourhood of the tumour, the impulses being then transferred to the bulbar nuclei of that nerve and thence to the pneumogastric nucleus.