f the
establishment of drainage. If the symptoms point to suppuration having
occurred between the bone and the dura, the skull should be trephined
and further bone removed with the rongeur forceps as may be required.

Time may be saved by separating the sequestrum with the aid of an
elevator or sharp spoon, or by chiselling away the dead part till
healthy vascular bone is reached.

#Tuberculosis# of the cranial vault is usually met with in children.
The disease commences in the diploe, and results in the formation of a
central sequestrum, around and beneath which the tuberculous process
spreads. Granulations form between the skull and the dura, and on the
outer aspect lifting up the pericranium. The sequestrum is slowly
thrown off, and when separated is circular like a coin and presents
worm-eaten edges.

A circumscribed, tender swelling forms, at first yielding an obscure
sensation of fluctuation, but later, when the pus is no longer
confined under the pericranium, assuming the characters of a cold
abscess, which gradually becomes superficial, and eventually bursts
through the scalp, forming one or more sinuses.

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 diploe, 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 s