The skull is very liable to solutions of continuity, in consequence of its exposure to mechanical injuries. In the infant it may be indented and fissured, or simply indented by the pelvis of the mother, or by the misapplication of instruments to facilitate the birth of the child. Various kinds of punctured and shot wounds, fracture and crushing of the skull, may take place at the spot to which violence has been directly applied; and at the same time bone may be depressed or fragments driven in (impressio et depressio); the tables may be separated and splintered; there may be fissure and contrafissure; the bones may be denuded of their covering of soft parts, or there may be simply concussion of the bone within a circumscribed space. Lastly, the openings made in the skull artificially with the trepan belong to the same class.

All these injuries are of a grave character, not only on account of the violence done to the brain and its membranes by the penetrating instrument or by depressed fragments of bone; but also independently of such complication, from the concussion which the brain and its membranes frequently suffer at the time of injury, as well as on account of the extravasation of blood which takes place immediately beneath the bone, or dura mater, or into the pia mater, or the brain. They may be rendered further serious, irrespectively of the foregoing causes, by the supervention of inflammation of the bone and dura mater, which is usually so much aggravated by the contusion and concussion that have generally happened as to go on to the production of pus and sanies, and readily pass from the external parts to the inner membranes of the brain.

Nevertheless, punctured wounds, fractures, and considerable injuries to the walls of the skull, even when combined with displacement of the fragments, do often heal by first intention, or by the way of suppuration. Fractured surfaces become soldered to each other by bony callus; or, after being rounded off by absorption or exfoliation, they are held together by means of a fibroid callus; and the fragments which perish, and are thrown off during the process of suppuration, are replaced by a similar tissue, in which new bone is sparely formed.

Sometimes one fissure exists alone, sometimes there are several; and, in the latter case, they may all start from one spot on a bone, or may be multiplied by the branching of a single fissure. They often terminate in a suture, which is then usually separated (diastasis), but not unfrequently they are continued across the suture into the adjoining bone. They generally do not unite for a considerable time, and may, even after the expiration of a very long period, exhibit no tendency to union; the rough edges of the fissure are merely rounded off by absorption. If they should then heal, the void is filled up by fibroid callus, which unites with the pericranium and dura mater. They are seldom repaired by means of bony callus, on the contrary, they are sometimes fatal; for the inflammation and suppuration which occur in their vicinity, and in which the inner membranes and the brain become involved, destroy life, it may be after a long period; or the same result ensues, sooner or later, from the various injuries which the brain and its membranes have sustained from the original violence. Large and numerous fissures are generally rapidly fatal, especially such as extend deep into the base, and those which take place from the skull being crushed.

A fall or a blow very frequently produces contusion, separation of the periosteum, or concussion of the bone at a circumscribed spot, while, at the same time, there may be no injury perceptible externally. The consequence is, that the periosteum inflames, pus or sanies is effused, and the outer lamella of the bone may die and exfoliate; or if the bone have been violently injured, it may inflame in its whole thickness, and the periosteum and dura mater with it, and pus or sanies may be produced, both upon the surface and in the substance of those structures: the bone then becomes discolored, and has a dirty grayish-green appearance, all its pores are filled with purulent or sanious matter, its surfaces particularly are rough, and seem corroded, and at length it perishes in its whole thickness. The inflammation of the dura mater very often spreads from its original seat to a considerable extent, and leads to the formation of numerous abscesses, which, after a time, become confluent, and also erode the vitreous table. At length the inflammation spreads to the inner membranes of the brain, or - the pus and sanies being taken up into the veins of the diploe, - either by meningitis or by metastasis, the injury proves fatal.

Openings in the skull, made with the trephine or by necrosis, are closed, as has already been remarked, by means of a fibroid plate, which usually ossifies incompletely or not at all. Complete ossification, when it does take place, always occupies a very long period.

The difficulty with which injuries of the skull are repaired by bony callus is worthy of remark; but the cause of the difficulty still requires a satisfactory explanation.

Fissures are sometimes met with in the cranial bones of new-born children, which extend several lines from the margin into the bone, and usually run a little obliquely through its thickness. It is important to mention them, in a forensic point of view, inasmuch as they bear considerable resemblance to the clefts and fissures which are produced by external violence, and may be confounded with them.