unicating with the arteries of the limb; the walls of the space
consist of the remains of the original tumour, plus a shell of bone of
varying thickness. The most common seats of the condition are the lower
end of the femur, the upper end of the tibia, and the bones of the
pelvis.

The _clinical features_ are those of a pulsating tumour of slow
development, and as in true aneurysm, the pulsation and bruit disappear
on compression of the main artery. The origin of the tumour from bone
may be revealed by the presence of egg-shell crackling, and by
examination with the X-rays.

If the condition is believed to be innocent, the treatment is the same
as for aneurysm--preferably by ligation of the main artery; if
malignant, it is the same as for sarcoma.

#Secondary Tumours of Bone.#--These embrace two groups of new growth,
those which give rise to secondary growths in the marrow of bones and
those which spread to bone by direct continuity.

_Metastatic Tumours._--Excepting certain cancers which give rise to
metastases by lymphatic permeation (Handley), the common metastases
arising in the bone-marrow reach their destination through the
blood-stream.

[Illustration: FIG. 153.--Epitheliomatous Ulcer of Leg with direct
extension to Tibia.

(Lord Lister's specimen. Anatomical Museum, University of Edinburgh.)]

Secondary cancer is a comparatively common disease, and, as in
metastases in other tissues, the secondary growths resemble the parent
tumour. The soft forms grow rapidly, and eat away the bone, without
altering its shape or form. In slowly growing forms there may be
considerable formation of imperfectly formed bone, often deficient in
lime salts; this condition may be widely diffused throughout the
skeleton, and, as it is associated with softening and bending of the
bones, it is known as _cancerous osteomalacia_. Secondary cancer of bone
is attended with pain, or it suddenly attracts notice by the occurrence
of pathological fracture--as, for example, in the shaft of the femur or
humerus. In the vertebrae, it is attended with a painful form of
paraplegia, which may involve the lower or all four extremities. On the
other hand, the disease may show itself clinically as a tumour of bone,
which may attain a considerable size, and may be mistaken for a sarcoma,
unless the existence of the primary cancer is discovered.

The cancers most liable to give rise to metastasis in bone are those of
the breast, liver, uterus, pr