=Treatment.= The displacement of the mastoid process is of so incomplete a nature that the question of replacement by open operation seldom arises. In the event, however, of intracranial complications, operative treatment must be carried out. Under ordinary circumstances the treatment consists mainly in the prevention of suppuration. When suppuration occurs, frequent cleansing of the ear must be carried out in order to prevent accumulation of pus in middle ear and antrum. This object is to be attained, not by syringing, but by gentle irrigation and light packing. Later on it may become necessary to carry out the complete mastoid operation. FRACTURES OF THE VAULT OF THE SKULL Fractures of the vault of the skull may be restricted to the vault or associated with a basic fracture. Evidence has been brought forward previously to show that many vault fractures may be regarded as mere upward extension from a primary basic lesion. The limitation of a fracture to the vault depends on the nature of the productive force, the degree of violence used, the site of application, and the direction of the force. Thus, the smaller the weapon, the greater the violence, the nearer the site of application to the vertex, the more direct the blow, the greater is the tendency to vault limitation. Again, compound fractures are much more liable to vault limitation than simple fractures, as is proved, for instance, by the reports of Sir Prescott Hewitt--20 compound fractures in which the fracture was restricted to the vault of the skull, and 56 simple fractures in which the base was involved in all but one. Fractures of the vault may involve:-- (_a_) the external table only; (_b_) the internal table alone; (_c_) the whole thickness of the skull. =Fractures of the external table alone.= These fractures are excessively rare. Their existence was even doubted till the recent South African War, when Makins[23] saw one case of this nature. They appear to be due to the impact of a glancing bullet (see p. 297). A ‘gutter-shaped’ depression results, the comminuted fragments of the external table being carried away or distributed in the region of the lacerated scalp (see Chapter IX).