ow that a considerable deposit of
lime salts may precede the formation of bone, as is seen in Fig. 111. In
course of time the vertebral column becomes rigid, the head is bent
forward, the hips are flexed, and abduction and other movements of the
arms are limited. The disease progresses by fits and starts, until all
the striped muscles of the body are replaced by bone, and all movements,
even those of the jaws, are abolished. The subjects of this disease
usually succumb to pulmonary tuberculosis.

There is no means of arresting the disease, and surgical treatment is
restricted to the removal or division of any mass of bone that
interferes with an important movement.

A remarkable feature of this disease is the frequent presence of a
deformity of the great toe, which usually takes the form of hallux
valgus, the great toe coming to lie beneath the second one; the
shortening is usually ascribed to absence of the first phalanx, but it
has been shown to depend also on a synostosis and imperfect development
of the phalanges. A similar deformity of the thumb is sometimes met
with.

Microscopical examination of the muscles shows that, prior to the
deposition of lime salts and the formation of bone, there occurs a
proliferation of the intra-muscular connective tissue and a gradual
replacement and absorption of the muscle fibres. The bone is spongy in
character, and its development takes place along similar lines to those
observed in ossification from the periosteum.

#Tumours of Muscle.#--With the exception of congenital varieties, such
as the rhabdomyoma, tumours of muscle grow from the connective-tissue
framework and not from the muscle fibres. Innocent tumours, such as the
fibroma, lipoma, angioma, and neuro-fibroma, are rare. Malignant tumours
may be primary in the muscle, or may result from extension from adjacent
growths--for example, implication of the pectoral muscle in cancer of
the breast--or they may be derived from tumours situated elsewhere. The
diagnosis of an intra-muscular tumour is made by observing that the
swelling is situated beneath the deep fascia, that it becomes firm and
fixed when the muscle contracts, and that, when the muscle is relaxed,
it becomes softer, and can be moved in the transverse axis of the
muscle, but not in its long axis.

Clinical interest attaches to that form of slowly growing
fibro-sarcoma--_the recurrent fibroid of Paget_--which is most
frequently met with in the muscles of the