As a comparatively small proportion of tumours of the brain--using the term "tumour" in its widest sense--are amenable to surgical treatment, it is only necessary here to refer to those aspects of this subject that have a distinctively surgical bearing. Various forms of growth occur in the brain, the most common being tuberculous nodules, syphilitic gumma, endothelioma, glioma, and sarcoma. Less frequently fibroma, osteoma, and parasitic, hæmorrhagic, and other cysts are met with. The growth may originate in the brain tissue primarily, or may spread thence from the membranes, or from the skull. In relation to operative treatment, it is an unfortunate fact that those forms that are well defined and do not tend to infiltrate the brain tissue, usually occur at the base, where they are difficult to reach; while those that develop in more accessible regions are for the most part infiltrating growths of a gliomatous or sarcomatous nature, and are therefore irremovable. _Clinical Features._--The presence of a tumour in the brain inevitably results sooner or later in an increase in the intra-cranial tension, and to this the symptoms are chiefly due. The earliest and most prominent of the _general symptoms_ are severe paroxysmal headache, optic neuritis, with choked disc and limitation of the field for blue, amounting sometimes to blue-blindness (Cushing). The relative degree of neuritis in the two eyes is a reliable guide to the side on which the tumour is situated (Horsley). The symptoms are seldom absent, and are common to all forms of tumour, wherever situated. Vomiting, which is without relation to the taking of food and is usually unattended by nausea, is a characteristic symptom when present, but it is wanting in two-thirds of the cases (Cushing). Vertigo, general convulsions, and signs of mental deterioration are also present in a considerable proportion of cases. In addition, certain _localising symptoms_ may be present. When, for example, the tumour is situated in the _cortex of the Rolandic area_, attacks of Jacksonian epilepsy, preceded by an aura, which is usually referable to the centre primarily implicated, are common. The group of muscles first involved, and the order in which other groups become affected, are important localising factors. As the tumour increases in size, these irritative phenomena are replaced by localised paralyses. The tactile and muscular sensations are also disturbed, and motor and sensory aphasia may be present. In some cases localised tenderness on percussing the skull may be of assistance in indicating the site of the tumour. When the tumour is _sub-cortical_, that is, in the centrum ovale, there are no Jacksonian spasms, the motor paralysis is more widespread, and sensation also is lost on the opposite side of the body. There is no special tenderness on percussion. It is not always possible, however, to distinguish between cortical and sub-cortical tumours, and in many cases both areas are invaded.