There is, however, no certainty about these fractures. Extensive fissures of the vertex are almost always extended to the base of the skull, while the reverse is seldom true. There are doubtless also many cases in which a bursting force compromises the bone rather than mere radiation of unexpended violence; but so long as skulls conform to no fixed mathematical figures nor proportions, and are composed of bones varying in shape, density, and strength, it will be impossible to formulate any laws which are sufficiently comprehensive to be satisfactory. Fractures in the posterior fossa occur most often through violence applied posteriorly and from below. There is a ring form of basal fracture produced mainly by the impact of the vertebral column, as when an individual falls upon his head the weight of the body forcing the cranial base in upon the brain.
PLATE XLII
Fractures of the Base of the Skull. Illustrative lines of fissure or fracture are printed in red.
Fractures of the anterior fossa may involve the roof of the orbit; even facial bones may participate in the injury. These considerations are not without importance, for if a patient presents symptoms of injury of the petrous bone, and if these be accompanied by injury to the lateral region of the skull, we are in a position to make a diagnosis of fracture of the middle fossa. (See [Plate XLII], and [Figs. 375] and [376].)
By all means the majority of basal fractures are mere fissures which open and close instantly upon their production—close so quickly, in fact, as scarcely even to include blood between the broken bony surfaces.