ise in differentiating such a mass of bone from
sarcoma; the ossification in muscle is uniformly hard, while the sarcoma
varies in consistence at different parts, and the X-ray picture shows a
clear outline of the bone in the vicinity of the ossification in
muscle, whereas in sarcoma the involvement of the bone is shown by
indentations and irregularity in its contour.

A similar ossification has been observed in relation to the insertion of
the brachialis muscle as a sequel of dislocation of the elbow. After
reduction of the dislocation, the range of movement gradually diminishes
and a hard swelling appears in front of the lower end of the humerus.
The lump continues to increase in size and in three to four weeks the
disability becomes complete. A radiogram shows a shadow in the muscle,
attached at one part as a rule to the coronoid process. During the next
three or four months, the lump in front of the elbow remains stationary
in size; a gradual decrease then ensues, but the swelling persists, as a
rule, for several years.

[Illustration: FIG. 111.--Calcification and Ossification in Biceps and
Triceps.

(From a radiogram lent by Dr. C. A. Adair Dighton.)]

Ossification in the adductor longus was first described by Billroth
under the name of "rider's bone." It follows bruising and partial
rupture of the muscle, and has been observed chiefly in cavalry
soldiers. If it causes inconvenience the bone may be removed by
operation.

Ossification in the deltoid and pectoral muscles has been observed in
foot-soldiers in the German army, and has received the name of
"drill-bone"; it is due to bruising of the muscle by the recoil of the
rifle.

_Progressive Ossifying Myositis._--This is a rare and interesting
disease, in which the muscles, tendons, and fasciae throughout the body
become the seat of ossification. It affects almost exclusively the male
sex, and usually begins in childhood or youth, sometimes after an
injury, sometimes without apparent cause. The muscles of the back,
especially the trapezius and latissimus, are the first to be affected,
and the initial complaint is limitation of movement.

[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 sh