TUMORS OF DOMESTIC ANIMALS i5 
surround a single tooth, but more often involves a number of teeth. 
It may occur as a group of cysts completely surrounded by a fibro- 
gelatinous dental sac and an alveolar bone capsule. It is sometimes 
described as odontosystoma. 
Bland-Sutton (3) has given a most complete description of seven 
different varieties of odontomas in man; but, as such varieties are not 
recognized in the domestic animals, no further reference will be 
made here. 
MYELOMA 
Definition. — Myelomas are neoplasms which are formed from red 
bone marrow. They vary in color from grayish to yellow, but may 
be pink and often are deep red. Myelomas occur as primary multiple 
growths in the cancellated portion of the sternum, ribs, and skull, 
and according to some authorities less frequently in the long bones 
except in the tibia, where it is admitted to be not infrequent. They 
are benign and slow growing. 
Structure. — The structure suggests a hyperplasia of the red 
marrow. During growth they induce active absorption of the bone 
and an invasion of the soft tissues. Microscopically these neoplasms 
consist of myelocytes, lymphocytes, erythrocytes, and a scanty 
amount of interstitial connective tissue. Often giant cells are pres- 
ent. The presence of giant cells was responsible for some patholo- 
gists' classifying the myelomas as myelosarcomas. They are fre- 
quently very vascular and rather liable to show hemorrhages. The 
naked-eye appearance and the microscopic appearance therefore 
suggest malignancy, though these neoplasms are invariably benign 
in nature and do not metastasize. There is a tendency of the 
hemorrhagic forms to become cystic. 
MYOMA 
Definition. — Myoma is a neoplasm composed of striated or non- 
striated muscle fibers and a variable amount of connective tissue. 
According to the variety of muscle, myomas are divided into leio- 
myoma, composed of involuntary or nonstriated muscle, and rhabdo- 
myoma, composed of voluntary or striated muscle. Of these two 
varieties leiomyoma is more common and occurs where involuntary 
muscle is normally present, as in the digestive tract, the reproduc- 
tive organs, and the urinary system, whereas rhabdomyoma fre- 
quently occurs in places where voluntary muscle doe's not exist nor- 
mally and is therefore considered to be of congenital origin. 
Appearance. — Myomas are firm, pale, globular, rounded, nodular, 
or diffuse structures which more rarely become pedunculated. They 
vary in size from a pinhead to a man's head and even larger. They 
are so similar to fibromas, with which they, frequently combine, 
that a differentiation can be made only by microscopic examination. 
This is especially true of myomas in the uterus. In this location 
they are often called fibroids until a microscopic examination proves 
them to be myomas. 
Myomas are surrounded by a connective-tissue capsule. They 
are slow growing, sometimes single, but more often multiple. 
Seats. — The most frequent seats are the muscle walls of the uterus 
and vagina in cows and hogs, and sometimes in dogs. The less 
