When they occur on the inner table, the func tion's of the brain are usually more or less dis turbed, although it would appear that the mental manifestations are not always implicated. In the skull of an idiot of advanced age, examined several years since by the writer of this article, there was a uniform deposition to the extent of nearly a quarter ofan inch; and in a recent autopsy of a young girl, he found the entire syncipital region very irregular in its surface, from being studded with variously-sized nodules, the bases of which flowed into and were lost in each other. This girl was of feeble intellect, and the victim of epilepsy. In the examination of a body at the Hotel Dieu, by Mr. King, that gentleman discovered on the petrous portion of the tem poml bone a tumour which he bad not been led to expect by any indication of suffering which. appeared during life. This tumour had the volume of a marble or pistol-bullet, was cel lular in its structure, and perfectly smooth on its surface ; a depression exactly correspondino. to it was found on the under surface of th'le middle lobe of the brain, but its substance and membranes had their normal characters.
The cranium is oftentimes found in the oppo site state of atrophy, in which the balance be tween deposition and absorption seems to have been disturbed, so much to the prejudice of the former, that the walls are sometimes not much thicker than a piece of paper. When- ever the two textures maintain their usual pro portion, this atrophy may be regarded as a natural abnormal state; but those cases in which either the inorganic or animal element preponderates, and a fragility or softening of the bone is thereby established, must be referred to some constitutional affection in which the rest of the osseous system has participated,, and the influence of which it will not fail to exhibit.
In addition to exostosis and hyperostosis, the cranium sustains other pathological changes as the effects of inflammation.
Previously to the establishment of osteitis, whether from a. common or specific cause, mercurial or syphilitic, there is found that stasis of the blood which always precedes inflam mation. The sanguineous complexion of the diphie in cases of erysipelas testifies that this engorgement may be produced by increased action in the neighbouring teguments.
It has already been stated that hypertrophy of the cranium may be regarded as a termina tion of osteitis. When inflammation is limited in its action and of long duration, it is probable that the ossific element is poured into the cells of the dipkie so as to effect their obliteration ; but when it is of a more vivid character, the opposite effect of softening (the precursor of ulceration) takes place, and both the outer and inner tables are rendered friable. This fre quently occurs to a great extent in the mastoidal cells, especially in children; and as, in them, the posterior portion of the meatus auditorius internus possesses an unclosed fissure, the dis charge which is consequent on the destruction of the cells is allowed an exit, before the mem brana tympani is destroyed ; although that, as well as the whole of the internal ear, is fre quently involved in the ravages of the disease— then, however, having passed into another ter mination of osteitis, viz. ulceration.
Adhesion can take place only where the cra nium has experienced a lesion from a mechani cal cause; and it is altogether prevented if the solution of continuity be great. The edges of a
wound, produced by a cutting instrument penetrating more or less perpendicularly to the surface of the bone, do not approximate; but they are united by an interposing callus as in the case of a common fracture, and the line formed by it is always visible in the same way as the cicatrix which persists after the ad hesion of soft parts. When a piece of the outer plate is elevated by a cutting instrument passing very obliquely to the surface of the bone, and the scalp is not detached, it will, on being immediately re-applied, unite with the surface from which it has been raised; and, if it be altogether removed, the reparation will be effected in the same way as in other parts, viz. by the granulation and cicatrization of the cut surface.
When there is loss of substance of the entire thickness of the bone, whether that loss be pro duced by mechanical or pathological causes, granulations spring up from the dura mater; the edge of the opening becomes very thin ; the surface cicatrizes and produces the appear ance of a dense fibrous membrane, the circum ference of which is attached to the margin of the hole and the adjacent pericranium.
Caries, which is analogous to ulceration of the soft parts, and is, in fact, an ulcerative ab sorption of bone, attacks the cranium in com mon with the rest of-the osseous system ; but it always first appears on one of the two tables, and not on the diploe, although ultimately the entire thickness is, in sorne cases, involved. Indeed, when it commences on the inner table, it is only by the extension of the ulcerative pro cess through the substance. of the bone, that the suppurative collection can be emancipated.
In this affection the pericranium is sometimes enormously thickened and almost inseparably attached to the rough biscuit-like surface of the bone beneath. In other cases, especially in those in which the ulcerative process has been provoked by mercury, it is in irregular patches; the pericranium is unattached and the denuded surface is of a dark colour.
Necrosis, or mortification of the bone, is of frequent occurrence ; but not in the way usually implied by that term. Whether it be the sub stance of the bone, or merely its outer lamina which is deprived of its Vitality, the reparation is not by a fresh deposition of bone, nor is it coeval with the separation of the necrosed part, as in the long bones ; but it is a subse quent action (such as has been already pointed out) which is established to supply the loss. Considerable portions of the frontal and parietal bones may thus be thrown off and the deficiency provided for by the granulations of either the subjacent diploe or the dura mater.
Medullary sarcoma sometimes manifests itself in the cranium. It appears to commence in the diploe by a deposition of tuberculous matter, which softens, and which in that state may be mistaken for pus ; the inorganic ele ment is withdrawn ; the accumulation con tinues and advances towards both tables, which in turn submit to the same change of structure; and, ultimately, a tumour is formed, the tapsule of which is constituted, on the one side by the pericranium, and, on the other, by the dura mater. In this tumour the knife detects spiculw of bone interspersed throughout its substance, and the edge of the opening which is left in the skull after maceration, is studded with irregular projecting points.