The skull, like the brain, may deviate in either direction from its proper size. In some cases it does not reach, in others it exceeds, its natural dimensions. Smallness of size may be general over the whole skull, or may be confined to some particular portion of it. Except when it is occasioned by protrusions of the brain beyond the bounds of the skull (encephalocele), it necessarily involves that the brain generally be small, or that portion of it be deficient or undeveloped; and in the latter case, the corresponding part of the skull is also wanting or but partially developed. The skull may be only relatively small, or it may be absolutely so: in the latter case the smallness of size occasions idiocy, and is a congenital state; a partial diminution is sometimes acquired subsequently to birth, particular parts of the skull becoming small and flattened, sinking in, and shrinking, when the corresponding portions of the brain are in a state of atrophy.

The bones of the face are of small size in cases of congenital hydro-cephalusf and their smallness is more striking in proportion to the enlargement of the cranium. A diminution in the size of the bones of the face is also observed in old age: it is chiefly due to wasting of the maxillary apparatus. And a similar attenuation is observed on one side of the face as a consequence of paralysis or neuralgia.

Increase of the size of the skull, when congenital, involves an excessive development of the brain, or, what is more frequent, hydrocephalus. The enlargement is mostly uniform and symmetrical, but in some exceptional cases the skull bulges in one direction or another, a particular section of it is more capacious than the rest, etc.

The dimensions of the skull rarely enlarge at any period after birth - that is, in the sense of increase of its capacity - without some appearance of absorption of the vitreous table, or separation of the sutures; still more rarely does it occur at mature age when the bones are completely formed, and almost never when the sutures are closed. It is seen occasionally at certain parts of the skull.

The bones of the skull and face are subject to many considerable variations in their thickness, sometimes being enlarged (hyperostosis), and sometimes attenuated. Hypertrophy usually commences with the bones of the cranium, it occurs in them frequently, and advances to a very considerable extent; whilst atrophy, especially that form which is peculiar to old age, is more common in the facial bones.

Hyperostosis almost always presents itself in both its forms, namely, that of deposition externally upon the bone, and simultaneous condensation of its tissue (sclerosis): in a few cases it goes on to such an extent, that the skull is not only, according to Jadelod and Ilg, larger than natural, misshapen, and uncommonly thick (9 lines to 1½ or 2 inches), but it also acquires a weight that is almost incredible. In the later periods of the disease, if not at its commencement, the thickening takes place at the expense of the cranial and adjoining cavities, - orbits, nares, labyrinths, and antra Highmoriana, - as well as of the foramina and fissures which are traversed by the nerves and vessels: the sutures also disappear. Other bones, and even the whole skeleton, may be increased in bulk, when the skull is thus affected; but the disease may be entirely confined to the skull, or even to the cranial bones alone, and those of the face, of other parts of the body, and the base of the cranium itself, may remain of their natural size. Not unfrequently, indeed, this hyperostosis of the cranium is associated with atrophy of the bones of the face and of the rest of the skeleton. In any case, it reaches its greatest extent in the cranial vault, and at its frontal and occipital portions: when it occurs in the bones of the face, it is most developed in the lower and upper maxillary bones. It may occur in early youth, in adult, or in advanced life, - a circumstance which depends partly upon the nature of the process.

«. It is sometimes the consequence of an overgrowth or excessive nutrition of the bone, the conditions of which are as yet unknown to us. It is generally developed slowly. It occurs chiefly in adult life; and frequently is associated with ivory-like exostosis on the outer table of the skull, with enlargement and prominence of the inner table, especially near the frontal ridge, and with a growth of bone upon the dura mater.

B. At other times it arises from an inflammation of the bone, which may be acute and recur from time to time, or may be chronic and continued. The pericranium on the one side, and the dura mater on the other, take part in the inflammatory process.

The first of these forms furnishes an exudation of bone upon the surface of the cranial bones, which varies in thickness, and presents the characters of the velvety, finely filamentous, and reticulated osteophyte: it gradually becomes identified with the bone, either with or without the intervention of a newly formed layer of diploe.

Processes of this kind mostly take place on the inner table of the skull, and especially upon and near those spots which are best supplied with vessels; they are, therefore, common along the sinuses and the sutural margins of the bones, and furnish the bone at those parts with a new vitreous table. Moreover, they are processes which occur chiefly in young persons. The exudation of bone, which is met with on the inner table of the skull in pregnant women, deserves an especial notice. It is so frequently observed in women under such circumstances, and advances in them to so great an extent, compared with what it reaches in other cases, that some connection between it and pregnancy must be admitted; and as it has been regarded with interest, since the time of its discovery in this Institution,11 devote the following paragraphs to an account of it.

The puerperal osteophyte, as it is usually termed amongst us, because we commonly observe it in persons who have died in consequence of the puerperal state, generally occupies the frontal and parietal bones: sometimes it is found covering the whole inner surface of the cranial vault, and in that case it may be noticed scattered in patches over the base of the skull also. But it does not usually occupy large extents of surface completely, even when it is of considerable thickness, the eminences on the inner surface of the skull, and more rarely the depressions, being left uncovered. Such bare spots on the vitreous table, whether they be situated on the eminences or depressions, are parts at which their own pressure, or that of the brain, has prevented the deposition of the exudation, and they are at once distinguished by having lost their polish and natural color.

1 Oestr. Med. Jahrbüch., vol. xv, p. 4.