The _lateral sinus_ may be laid open in any part of its course, more especially at the angle of junction between the lateral and sigmoid sinuses, in close relation to the occipito-mastoid suture, a region not infrequently involved in basic fractures. The blood effused will occupy the supra- or infra-tentorial spaces according to the situation of the rent in the sinus-wall. The _cavernous sinus_ is frequently involved in anterior and middle fossa fractures. The blood effused usually escapes into the nose and mouth. [Illustration: FIG. 55. A COMMINUTED FRACTURE OF VAULT AND BASE, THE BASIC FRACTURE INVOLVING BOTH MIDDLE AND POSTERIOR FOSSÆ. The middle fossa fracture, on the left side, follows the usual course. The posterior fossa fracture resulted in laceration of both lateral sinuses--at the usual site, junction of sigmoid and lateral sinuses. Probes are inserted at each site of laceration. The resultant hæmorrhage was mainly intradural, but, as is seen in this figure, the dura mater of the posterior fossa is stripped away from the bone by an extra-dural extravasation.] =Symptoms.= The rapid diffusion of blood throughout the subdural space, and the usual coexistence of extensive injury to bone and brain, seldom permit of the development of such definite symptoms as might accurately define the localization of the hæmorrhage. The most important feature in the diagnosis lies in the fact that compression symptoms are early in onset and progressive in nature. The ‘lucid’ interval, so prominent a feature in middle meningeal extravasations, is either absent or of such short duration as to be difficult of recognition. The rapid development of symptoms pointing to brain compression, and the nature of the injury itself should enable the surgeon, in the majority of cases, to come to the conclusion that the patient is suffering from diffuse subdural hæmorrhage. In all cases of doubt, lumbar puncture should be carried out, the presence of blood-corpuscles in the cerebro-spinal fluid confirming the diagnosis. =Indications for operation.= Whether one considers the case from the point of view of the more immediate prognosis or from the more remote aspect of the case, operation is indicated, if the condition of the patient is compatible with such treatment. In considering the advisability of adopting an active form of treatment, it must be taken into account that, if the patient recovers without operation, the presence of an extensive subdural blood-clot must necessarily interfere, as an after-result, with the functions of the cortex, and that the removal thereof affords considerable hope of permanent cure. =Operation.= Operative measures may be considered as follows:-- The treatment of the fracture and of the dural rent. The treatment of the subdural extravasation.