The cranial bones are frequently the seat of these processes, which may be set up not only by violence, but by many other external influences, and very frequently by some internal cause. Sometimes, also, they are occasioned by a previous disease of the bone itself, or by inflammation, suppuration, ulceration, etc, of neighboring parts.

I have stated, in my previous remarks, that inflammation frequently gives rise to an increase of bulk, to hyperostosis of the skull (p. 129). Syphilis, which is a very frequent cause of the enlargement, attacks particularly the frontal and parietal, amongst the bones of the skull, and the nasal bones and alveoli, in the face; and it very generally leads to extensive caries and necrosis. Caries and necrosis, when induced by tuberculous disease, are, also observed on the frontal, parietal, and nasal bones; but they are more frequent at the base of the skull, especially in the body of the sphenoid.

As, on the one hand, inflammation may extend from the seat of these processes to the meninges and the brain, so on the other, are they sometimes themselves occasioned by inflammation of the membranous parts of the internal ear, or of the nares and adjoining cavities, or by inflammation of neighboring, ligamentous tissues and bones. Thus, for instance, caries of the occipital bone may be caused by inflammation and suppuration of the cervical vertebrae, and of their ligamentous apparatus, and the bones of the face suffer almost incredible devastations from so-called facial cancer.

3. Expansion, Softening, And Consecutive Induration

Rickets not unfrequently, when met with in the infant, exists in a pre-eminent degree in the skull. It may be recognized by the great development of the prominences of the cranial bones, by the small denticulations and sinuous line of the sutures, and by the great thickness, the succulence, the cancellous expansion, the softness, and the great vascular fulness of the bones. It extends to the base of the skull, and, in a small degree, to the bones of the face also. The swelling of the wall of the skull effaces the inequalities of its inner surface, and it is remarkably smooth: the processes which are situated at the inner surface of the base of the skull, are unusually thick and smooth.

No less uncommon is that form of expansion (osteoporosis) resembling rickets, which affects the skull chiefly, and is indeed generally confined to that part, but which prevails at a later period of life than rickets, and occurs even in advanced age. It reaches, as has been already remarked, a very considerable degree, and terminates in a peculiar and very marked induration of the cranial bones.

When mollities ossium is general throughout the rest of the skeleton, it may affect the skull also; but it always does so in a subordinate degree.

4. Adventitious Growths

After the statements which have been made with respect to the occurrence of these growths in the osseous system generally, it is unnecessary, in this place, to do more than to remark, that cancerous growths do frequently form in the skull, as well on the calvarium as at the base: they may all be included, in brief, in the term "Fungus Cranii." They are commonly supposed to be malignant, i. e. cancerous, diseases of the cranial bones; but the above-mentioned distinguishing term was given them at a time when an attempt was made to prove the existence and the origin of the same morbid growth in the skull, as had before then been considered peculiar to the dura mater, and had long been named "Fungus Duroe matris." The two diseases may be readily confounded during life, especially when the disease of the bone commences in the diploe; for it breaks through the outer table as it grows, and spreads through an aperture bounded by bone over the surface of the skull.