ostate, colon, and rectum; hyper-nephroma
of the kidney may also give rise to metastases in bone.

_Secondary tumours derived from the thyreoid gland_ require special
mention, because they are peculiar in that neither the primary growth in
the thyreoid nor the secondary growth in the bones is necessarily
malignant. They are therefore amenable to operative treatment.

_Secondary sarcoma_, whether derived from a primary growth in the bone
or in the soft parts, is much rarer than secondary cancer. Its removal
by operation is usually contra-indicated, but we have known of cases
terminating fatally in which the _section_ revealed only one metastasis,
the removal of which would have benefited the patient.

In all of these conditions, examination of the bones with the X-rays
gives valuable information and often disclose unsuspected metastases.

_Cancer of Bone resulting from Direct Extension from Soft Parts._--In
this group there are also two clinical types. The first is met with in
relation to _epithelioma of a mucous surface_--for example, the palate,
tongue, gums, antrum, frontal sinus, auditory meatus, or middle ear.
They will be described under these special regions.

The second type is met with in relation to _epithelioma occurring in a
sinus_, the sequel of suppurative osteomyelitis, compound fracture, or
tuberculous disease. The patient has usually had a discharging sinus for
a great number of years: we have known it to last as many as fifty. The
epithelioma originates at the skin orifice of the sinus, and spreads to
the bone and into its interior, where the progress of the cancer is
resisted by dense bone, which obliterates the medullary canal. Although
its progress is slow, the infiltration of the bone is usually more
extensive than appears externally. It is recognised clinically by the
characteristic cauliflower growth at the orifice of the sinus, and by
the offensive nature of the discharge. A similar epithelioma may arise
in connection with a _chronic ulcer of the leg_. The cancer may infect
the femoral lymph glands. The operative treatment is influenced by the
extent of the disease in the soft parts overlying the bone, and consists
in wide removal of the diseased tissues and resection of the bone, or in
amputation.

#Cysts of Bone.#--With the exception of hydatid cysts, cysts in the
interior of bone are the result of the liquefaction of solid tissue;
this may be that of chondroma, myeloma, or sarcoma, but mo