A prize-fighter was knocked out by a blow on the right side of the head, dying a few hours later. The post-mortem revealed no fracture of vault or base, but a linear laceration of the brain on the mesial aspect of the right hemisphere which exactly corresponded to the free margin of the falx cerebri. In this case, therefore, conclusive evidence was obtained that the brain had been driven from right to left against a firm and resisting barrier, corresponding laceration resulting. The lacerated area is usually cone-shaped, the base corresponding to the surface of the brain, the apex facing towards the lateral ventricles. In the most severe cases the anterior or lateral horns of the lateral ventricles may be involved at the apex of the cone, and, in the event of further cerebral softening, the horns of the ventricles may, as it were, bulge outwards, thus assisting in the formation of those traumatic cephaloceles that communicate between the lateral ventricle and the surface of the brain. On the other hand, if the degree of laceration be slight and the injury compatible with life, organization and partial resolution takes place, with the formation, in nearly all cases, of adhesions between the cortex and the membranes, of false membranes, arachnoid cysts, and of blood cysts. In the more serious cases cerebral fibrosis results, in direct proportion to the degree of cerebral destruction, with corresponding degeneration, both of the cerebral cortex and of the tracts that evolve therefrom. =Symptoms.= Certain regions of the brain may, when injured, give rise to localizing symptoms. More generally, however, all localizing features are obscured by an overpowering element--the presence of concussion, irritation, or compression of the brain. Still, in some cases, the localizing features are sufficiently marked, at some period of the case, to allow of a more definite diagnosis. The symptoms, therefore, must be considered under the two heads, (A) _localizing_, and (B) _general_. A. Localizing symptoms. _Localizing to the frontal lobes._ Phelps,[33] from a series of 130 cases, arrived at the following conclusions--that, ‘in nearly every case in which consciousness was retained or regained, and the mental faculties not perverted by general delirium, laceration of the left frontal lobe was attended by default in intellectual control, and that the lesion was usually of the anterior region and implicated its inferior surface.’ ‘Subcortical disintegration was characterized by abrogation of mental power, and superficial laceration by aberration in its manifestations.’ And secondly, that, ‘in nearly every instance in which laceration was confined to the right side, the mental faculties remained unaffected, except as they were obscured by delirium and stupor occasioned by coincident general lesion.’