The _treatment_ of compression is considered with the different lesions which cause it; the principle in all cases being to remove, if possible, the cause of the increased pressure within the skull. #Traumatic Œdema.#--In practice, cases are frequently met with, particularly in children, that do not conform to the classical description of either concussion, cerebral irritation, or compression. The injury may be followed by a varying degree of concussion which soon passes off but leaves the patient in a listless, drowsy state that may persist for days or even for weeks. The cerebration is disturbed, so that while the patient is not unconscious, he is apathetic and has lost his bearings and fails to recognise where or with whom he is. He complains of headache, there is tenderness on percussion over the skull, the knee jerks are diminished or absent, but there is no motor paralysis. In some cases there are localised jerkings, in others generalised convulsive attacks during which the patient becomes deeply cyanosed. The condition differs from compression due to middle meningeal hæmorrhage in that it is less severe and is not steadily progressive. When the symptoms are localised, the condition is probably due to œdematous infiltration of the injured portion of brain; when generalised, to increased intra-cranial tension from serous effusion into the arachno-pial space. The _treatment_ consists in diminishing the intra-cranial tension by purgation, leeches, bleeding, or lumbar puncture, or if life is threatened, by opening the skull over the seat of injury, or failing evidence of this, by a decompression operation in the temporal region. INTRA-CRANIAL HÆMORRHAGE Apart from the hæmorrhage that accompanies laceration of brain tissue, bleeding may occur inside the skull, either from arteries or from veins. The effused blood may collect either between the dura mater and the bone (_extra-dural hæmorrhage_), or inside the dura (_intra-dural hæmorrhage_). #Middle Meningeal Hæmorrhage.#--The commonest cause of extra-dural hæmorrhage is laceration of the middle meningeal artery. This artery--a branch of the internal maxillary--after entering the skull through the foramen spinosum, crosses the anterior inferior angle of the parietal bone, and divides into an anterior and a posterior branch which supply the meninges and calvaria (Fig. 186). Either branch may be injured in association with fractures, or from incised, punctured, or gun-shot wounds. The vessel may be ruptured without the skull being fractured, and sometimes it is the artery on the side opposite to the seat of the blow that is torn. The most common situations for rupture are at the anterior inferior angle of the parietal bone, in which case the anterior branch is torn (90 to 95 per cent.); and on the inner aspect of the temporal bone, where the posterior branch is torn (5 to 10 per cent.).