16 BULLETIN 1449, TJ. S. DEPARTMENT OF AGRICULTURE 
frequent locations are the esophagus, stomach, and intestines in 
horses and cows, the urinary bladder in dogs, and the serous mem- 
branes. The rarest place in domestic animals, but not in man, is 
the skin. Here myomas originate from the erector piliform muscles 
of the skin, from the ducts of the sweat glands, from the nipples, 
or from blood vessels. 
Structure. — Microscopically, myoma consists of spindle-shaped 
cells with rod-shaped or cylindrical nuclei. The cells are arranged 
in compact bundles which interlace with one another at various 
angles. The individual cells are held together by a small quantity 
of cement substance which is collagenous in nature. At times 
myoglia fibrils have been seen lying alongside of the cells. It is 
very important to distinguish the spindle-shaped cells of involuntary 
muscle of leiomyoma from the spindle-shaped cells of soft fibroma 
and the spindle-shaped cells of spindle-cell sarcoma, as the last two 
varieties often enter into combination with the leiomyoma and it is 
not easy to distinguish them. The muscle cells of leiomyoma are 
usually long, slender and sharply outlined, terminating in a pointed 
extremity. Their nuclei are long, rod shaped, with rounded ends, 
and lie within the cell body. Sometimes the muscle cells, as in blood 
vessels, are short and plump. 
The fibroblasts of the cellular fibroma, although spindle shaped, 
are shorter, and in those places where they form strands or bundles 
the very character of fibrous tissue is apparent. The principal 
distinction, however, lies in the fact that the nucleus of the cellular 
fibroma is short and oval and is peripherally situated. The small- 
sized neoplasms are much more likely to be pure myomas, while 
with the increase in size the fibromatous elements predominate in 
proportion to the diminution in the amount of involuntary muscle. 
It is for this reason that many of the uterine neoplasms which in 
reality are fibromyomas are commonly called fibroids. Leiomyoma 
may be distinguished from spindle-cell sarcoma by greater regularity 
in the direction of the cells, but particularly by the oblong rod- 
shaped outline of the nucleus, which is characteristic of leiomyoma. 
Combinations. — Myomas frequently combine with other neo- 
plasms, the most frequent combinations being fibromyomas, myxo- 
myomas, myosarcomas, and adenomyom&s. 
Degeneration. — Calcification is the most common change. Myxo- 
matous change may occur in myomas, which have a preponderance of 
fibrous connective tissue. Very rarely telangiectasis may be present 
in the peripheral parts of certain myomas, while the central part of 
the large neoplasms may be so poorly nourished that hyaline and 
later necrotic change may set in and result in cystlike softening. 
Nature. — Myomas are slow growing, encapsulated, benign, non- 
metastatic neoplasms. In combination with sarcoma they become 
malignant, produce metastases, and grow fairly rapidly. 
RHABDOMYOMA 
Description. — Rhabdomyoma is a rare neoplasm in both man and 
domestic animals. The characteristic tissue from which it derives 
its name is striated or voluntary muscle, which is always subordinate 
to other tissues, especially fibrous comiective tissue and cells resem- 
