The abscess should be laid open, all tuberculous granulations scraped away, and the sequestrum removed, with the aid of the chisel if it has not already become loose. On inserting the finger through the opening, it appears to penetrate to an alarming extent; this is due to the accumulation of tuberculous material between the skull and the dura mater, depressing the latter. After healing is completed, a depression or gap in the bone remains. #Syphilis.#--Syphilitic affections occur during the tertiary period of the disease, and usually implicate the frontal and parietal bones (Fig. 202). They are described in Volume I., p. 462. [Illustration: FIG. 202.--Skull of woman illustrating the appearances of Tertiary Syphilis of Frontal Bone--Corona Veneris--in the healed condition.] #Tumours.#--_Osteoma_ of the skull has been described with diseases of bone (Volume I., p. 481). _Sarcoma._--All forms of sarcoma are met with, implicating the bones of the skull. They may originate in the pericranium, in the diploë, or in the dura mater, and usually involve the bones of the vault. They sometimes occur in children (Fig. 203). [Illustration: FIG. 203.--Sarcoma of Orbital Plate of Frontal Bone in a child at age of 11 months, and 18 months. (Mr. D. M. Greig's case.)] The tumour grows chiefly towards the surface, but it also tends to invade the cranial cavity, and may thus assume the shape of a dumb-bell. Its growth is usually rapid, and results in the formation of a diffuse soft swelling, which sometimes pulsates, and sooner or later fungates through the skin. On account of its rapid growth the tumour is liable to be mistaken for an abscess, and in some cases the nature of the disease is only discovered after making an exploratory incision, and finding that the finger passes through a softened area in the bone. When the cranial cavity is encroached upon, signs of compression ensue. After the tumour has fungated, infective complications within the skull are liable to develop. In all cases the prognosis is extremely unfavourable. If diagnosed sufficiently early, an attempt may be made to remove the tumour, but often the operation has to be abandoned, either on account of the hæmorrhage which attends it, or because of the extent of the disease. The bones of the skull may become the seat of _secondary growths_ by the direct spread of cancer from the soft parts, _e.g._ rodent cancer (Fig. 204), or by metastasis of cancer or sarcoma from distant parts of the body, or of thyreoid tumours. Metastatic cancer would appear to be conveyed by the blood stream; it may occur in a diffuse form--cancerous osteomalacia--softening the calvaria so that at the post-mortem examination it may be removed with the knife instead of the saw; or it occurs in a discrete or scattered form, and then the macerated skull presents a number of circular and oval perforations.