Atrophy is, in some instances, confined to certain portions of the skull; it then presents itself either in the form of diminution of particular parts of the cavity of the skull, or of other cells and cavities in the cranial and facial bones; or it arises, as has been already remarked, from palsy, neuralgia, exhausting reparative processes after injuries, caries, etc.

Absorption of bone (Usura, Detritus) occurs very, frequently, and reaches a very advanced degree, in the bones of the skull. In the cranium, when confined to circumscribed spots, it is mostly induced by cancerous growths, such as fungus of the dura mater, or by morbid enlargement of the pituitary gland: when it extends over the whole inner surface of the skull, it arises from hypertrophy, or some displacement of the brain.