The layer of new bone varies in thickness, from that of a very thin film to half a line, a line, or more. It is usually thickest along the sutures, the longitudinal furrow, and the grooves for the arteria meningea media; it always becomes thinner towards its margins, and is lost in a delicate film.

Its color presents various shades and modifications of red; it almost always becomes paler towards its margin, and at that part is reddish white, white with red beneath, shining through it, or quite white. This depends on the age of the exudation, on the progress which it has made in its change into cartilage and bone, and on the development of a diploetic tissue within it.

It exhibits in its texture the same stages of development as any other ossific exudation.

(1.) It is at first a whitish-red or yellowish-red, gelatinous exudation, which is becoming vascular; it can be easily removed from the bone, and the vitreous table beneath is found to be natural, or to have merely lost some of its polished appearance.

(2.) It is a soft, flexible, cartilaginous lamina, full of minute pores; the vitreous table beneath is generally distinctly rough, or at any rate has its pores manifestly enlarged.

(3.) At the commencement of this stage it forms a flexible lamina, which is smooth and very finely porous, where it is opposed to the dura mater, while on the side which joins the vitreous table it is rough, cellular, and partly cartilaginous, partly osseous. A sanguineo-serous fluid oozes, under pressure, out of its numberless minute pores; and the cellular spaces on the opposite side are filled with a yellowish-red jelly, and sometimes with a clear-red bloody fluid. It is firmly adherent, and is seen, when an attempt is made to remove it, to be united to the vitreous table by the numerous lamellae and meshes of the cancellous, succulent tissue before mentioned; both these and numerous vessels are torn in separating the osteophyte.

The new growth is not developed beyond this point during pregnancy, or during any morbid puerperal condition which may succeed parturition; but at a later period it ossifies completely, and forms an integral part of the wall of the skull; it becomes, in fact, a new vitreous table, in some instances being dense (sclerosed) all through, in others united to the old vitreous table by an intervening cancellous layer. Generally, when the calvarium is removed, the new growth clings to the inner surface of the skull; but sometimes it separates from the skull, and remains adherent to the dura mater.

When the exudation is more than usually thick and extensive, a similar, but thinner, stratum is found on the outer table of the skull: at this part, also, as on the inner table, it appears to select the frontal and parietal bones, and is deposited chiefly along the coronal and sagittal sutures, and along the part at which the temporal muscle is attached, and the linea semicircularis; it may even be found on the external surface of several of the bones of the face, especially on the superior maxillary and nasal.

That there is no connection whatever between this new growth and the puerperal diseases of which the patients died, will be perceived from the following observations.

It presents itself in all its varieties of extent, thickness, and internal development, in the most rapid instances of puerperal disease: it is met with in cases of speedy death from rupture of the uterus during parturition, and when hemorrhages from that organ, during or after labor, have quickly exhausted the patient, as well as when Asiatic cholera, in its swiftest course, has carried off a woman during her pregnancy. The fact is more clearly proved from these growths being found in persons who, either during their confinement, or soon after it, have died of a disease quite independent of the generative organs, and one which may have arisen a long or a short time before the end of pregnancy, or even during labor, such, for instance, as pneumonia, phthisis, cholera, or apoplexy. Again, there are other cases still more convincing, in which the growth is found in healthy pregnant persons, who have met with unexpected and sudden death at an advanced period of pregnancy. But the fullest conviction is afforded by the discovery of this growth in females, who, at any period of their pregnancy, back to the third month, have died in a rapid or sudden manner.

The osseous growth under consideration, therefore, in pregnant and parturient women, is a phenomenon which, under circumstances hitherto unknown, is attendent on, and originates from, the pregnant condition.

The question as to the period of pregnancy at which the growth commences, is answered by the fact of its having been met with in every month as far back as the third: on one occasion, in which pregnancy was over, and the woman had been confined, it was but little developed, and existed only at a few small spots; on other occasions, at early periods of pregnancy, it extended over large tracts of the skull, its thickness was considerable, and its texture well developed. Its commencement, therefore, cannot be fixed at any definite period of pregnancy.

The exudation when completely ossified, and united with the old vitreous table, increases the mass of the skull in a degree commensurate with its own thickness; and this, of course, is very evident in cases of repeated pregnancy, in which several exudations have been deposited. And a highly instructive fact may be noticed in cases of this class, that some one of the more recent laminae of bone does not lie in immediate contact with the older layer, but is connected with it by an intervening stratum of diploetic tissue. In those cases in which the dura mater shares in the process, that portion of exudation which it supplies becomes a vascular cellular tissue, and is either spread out as such uniformly, or collected in patches here and there; and the new osseous lamina, being both perforated by the numerous vessels of the cellular tissue and grooved by them as they wind along its surface, does not possess so smooth and polished a surface as the original vitreous table; the dura mater and the skull, therefore, are more intimately connected, and adhere to each other more closely than natural. This connection is most firm, as might be gathered from my earlier remarks, along the sutures and sinuses, and especially near the longitudinal sinus.

What has been said establishes the existence of a puerperal hyperostosis of the skull, and its connection with repeated pregnancies.

In contrast with the frequency with which this growth is found in the bodies of women who either are pregnant or have been recently confined, it is quite rare in other persons, especially in men, to meet with a new formation of bone resembling it in situation, extent, or form. I can recall altogether but eighteen such cases, and the persons in whom it occurred were most of them young, and had died of very various diseases. Exudations indeed are deposited on the vitreous table in both sexes and at all ages; but they are less extensive than the puerperal osteophyte, and are usually confined to the neighborhood of the longitudinal furrow. And very frequently, and even commonly, they are already transformed into a layer of bone, are porous, and covered with serpentine furrows, and have adherent to them a growth of organized cellular tissue, which springs from the dura mater.

The remaining exudations of bone which take place upon the inner surface of the skull resemble needles, splinters, and plates; or they appear as if they had been dropped or poured upon the bone in a fluid state, and had then coagulated.