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 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).
=Fractures of the internal table alone.= Ambrose Paré drew attention to this class of fracture in 1652, but it remained for Teevan to investigate more fully the condition in 1865. Previous to Teevan’s investigations, it had been considered that the internal table of the skull was the more brittle, and that fractures confined to the internal table were to be explained on that hypothesis. Teevan, however, demonstrated the incorrectness of such a theory, for, on firing bullets through the skull, from without inwards and from within outwards, it was found that on all occasions the more distal table suffered the more severely. This was explained in the following manner:--the fracture of the proximal table was produced by the bullet, whilst that of the distal table resulted, not from the passage of the bullet alone, but also from various fragments of bone driven along with the bullet.