[Illustration:  FIG. 112.—­Ossification in Muscles of Trunk in a case of generalised Ossifying Myositis.

(Photograph lent by Dr. Rustomjee.)]

The affected muscles show swellings which are rounded or oval, firm and elastic, sharply defined, without tenderness and without discoloration of the overlying skin.  Skiagrams show 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 abdominal wall.  A rarer variety is the ossifying chondro-sarcoma, which undergoes ossification to such an extent as to be visible in skiagrams.