Class A. Subdural hæmorrhage, apparently without other serious injury to bone or brain. 36 cases. 22 recovered after operation. 14 died--11 without and 3 after operation. Class B. With serious brain-injury. 36 cases. 6 recovered after operation. 30 died--10 without and 20 after operation. In other words, every case died in which no operative measures were adopted, whilst after operation 28 recovered and 23 died. My own experience is limited to 4 cases, 3 of which recovered. =Pia-arachnoid hæmorrhage.= From evidence obtained at post-mortem examinations, it may be concluded that the great majority of cases of severe head-injury--especially those in which ‘irritation’ of the brain is a prominent feature--are associated with pia-arachnoid hæmorrhage. This is evidenced by the presence of a film of blood and serum over certain regions of the brain, not confined to the region subjacent to the skull area primarily involved, but also present over the opposite pole of the brain (injury by contre-coup). Subpial hæmorrhage differs from the subarachnoid variety in that the blood follows the invaginations of the pia mater, lining, therefore, both major and minor cerebral sulci. Subpial and subarachnoid hæmorrhages are, however, generally co-existent, and the term--pia-arachnoid hæmorrhage--aptly describes the conditions commonly found. The =symptoms= resulting from such blood extravasations are such as are described in the sections dealing with concussion and irritation of the brain (see p. 166). INJURY TO THE BRAIN Injury to the brain must always be regarded as by far the most important of the many complications associated with fracture of the skull. A fracture is not necessarily accompanied by brain-injury, and laceration of the brain may exist without a fracture. There can, however, be no question that the more severe cases of head-injury are almost invariably associated with some degree of brain-injury--varying from contusion to extensive laceration, cortical or central. No part of the brain is exempt from injury, but two regions, the antero-inferior aspect of the frontal lobe and the antero-external aspect of the temporo-sphenoidal lobe, show a special liability to contusion and laceration. The brain may be injured immediately subjacent to the site at which the blow is delivered (direct injury), or at the pole directly opposite that at which the blow was applied (indirect injury). Direct injury results from the in-driving of comminuted and depressed fragments of bone, from the passage of a foreign body, and from the direct transmission and diffusion of forces through the subjacent cerebral substance.