Chronic Inflammation gives rise to a considerable thickening and induration of the walls of the skull, and irregularity and roughness of their surface, with, sometimes, an almost monstrous thickening and fibro-lar-daceous condensation of the pericranium on the one side and the dura mater on the other.

This class of disease includes also the hyperostosis of the cranial bones, which originates in their infection with syphilis.

y. Lastly, the increase of volume, or hyperostosis, may be the induration consecutive upon a rickety state of the bones of the skull, or upon the expansion of bone which resembles that of rickets, but commences at later periods of life. The latter cases are distinguished by the chalky appearance and dull white color of the substance of the cranial bones, and by the coarse grain of their fracture: their surfaces are rough, and the inner table especially exhibits permanently enlarged pores and deep impressions for vessels.

The most extreme cases of hyperostosis are those of chronic inflammation, and the last mentioned consecutive induration. All the rare instances of enormous thickening and induration of the cranial bones appear to be of that nature.

The principal example of partial hyperostosis is the ivory-like exostosis which is frequently observed on the skull. It is almost always combined with considerable induration of the cranial bones. On the inner table, in the neighborhood of the frontal suture, there frequently exist smooth, or rough and striated elevations, which are produced by local expansion and subsequent induration of the skull. Finally, plates or rounded masses of bone, mostly of small size, are sometimes found glued on, as it were, in rugged depressions, on the inner table: they were originally productions from the dura mater.

By far the greatest number of cases of atrophy of the skull are those which are peculiar to old age. The bones chiefly affected are the facial, and of these most commonly the maxillary bones. It is an atrophy associated with wasting of the whole skeleton.

A remarkable attenuation of the wall of the skull occurs symmetrically at the top of the parietal bones in old and decrepit persons. At an oval or elliptical spot, the diploe shrinks to such an extent, that the two compact tables unite with one another, and constitute a translucid layer not thicker than a sheet of paper. The diploe around accumulates, so that the bone is thickened externally by an uneven swelling. No internal cause for the appearance has as yet been discovered, though it appears to me not improbable, that it has some connection with inveterate syphilis.