Myoma is a tumor composed of newly formed muscle-fibers. According as to whether the muscle is striped and voluntary, or unstriped and involuntary, we have the rhabdomyoma and the leiomyoma.

The first is very uncommon, but occurs in the kidney, heart, and uterus.

The latter occur frequently in the uterus and broad ligament, but may arise wherever there is involuntary muscle.

Fig. 51. - Osteoma of the Lung. X 75 (Dürck).

1, Bone-trabeculae; 2, fibrous interspaces not presenting the characters of medullary spaces.

May be single or multiple. Are firm, round, lobulated growths, dark reddish in color. Microscopically they consist of elongated spindle cells, with rod-shaped nuclei collected in bundles that interlace in all directions.

Are benign, slow of growth, and frequently undergo cystic or calcareous degeneration. The cysts contain mucus.

Usually are in combination with fibroma.