[Illustration:  FIG. 110.—­Ossification in Tendon of Ilio-psoas Muscle.]

Traumatic Ossification in Relation to Muscle.—­Various forms of ossification are met with in muscle as the result of a single or of repeated injury.  Ossification in the crureus or vastus lateralis muscle has been frequently observed as a result of a kick from a horse.  Within a week or two a swelling appears at the site of injury, and becomes progressively harder until its consistence is that of bone.  If the mass of new bone moves with the affected muscle, it causes little inconvenience.  If, as is commonly the case, it is fixed to the femur, the action of the muscle is impaired, and the patient complains of pain and difficulty in flexing the knee.  A skiagram shows the extent of the mass and its relationship to the femur.  The treatment consists in excising the bony mass.

Difficulty may arise 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.