TUMORS OF DOMESTIC ANIMALS 17 
bling sarcoma. The greater part of the neoplasm may not contain any 
striated muscle fibers. Only here and there isolated fibers, or groups 
of striated fibers, may be present. Rhabdomyoma usually occurs in 
places where striated muscle is not normally present, except in the 
heart. 
Seats. — The most common seat by far is the kidney, then the tes- 
ticle, heart, vagina, uterus, bladder, and parotid gland. A case was 
reported found in the lung of a young sheep. The presence of this 
neoplasm in places where no voluntary muscle normally exists is an 
indication of congenital origin. In the kidney rhabdomyoma 
reaches the largest size, appearing as a rounded or irregular mass, 
which may lead to a total destruction of the organ. Rhabdomyomas 
of the testicle are not so large as those of the kidney and are less 
destructive. The rhabdomyomas of the heart are frequently pedun- 
culated. . 
Structure. — On microscopic examination the striated fibers in 
rhabdomyomas are smaller than normal muscle fibers, more irregu- 
lar, and often spindle shaped, or even club shaped. The sarcolemma 
is generally present and often droplets of glycogen can be demon- 
strated. The striation of the muscle fibers is faint and in places 
may be entirely absent. Fibrillar connective tissue and spindle- 
shaped, sarcomalike cells, some of which are suggestive of embryonal 
muscle cells, predominate. 
Nature. — Rhabdomyomas are malignant in proportion to the 
amount of sarcomalike element which they contain. Adenomatous 
elements may be present, in which case the neoplasm is practically 
benign. 
NEUROMA 
Definition. — Neuromas are neoplasms composed of newly formed 
nerve tissue. The term is indiscriminately applied to any new 
formation occurring in the course of nerves. A distinction there- 
fore should be made between the neoplasms consisting of nerve fibers, 
ganglion cells, or both combined, which are the true neuromas, and 
neoplasms without any increase in nerve fibers or ganglion cells. 
The latter are composed merely of a fibroconnective tissue enlarge- 
ment or overgrowth on a nerve trunk, and are false neuromas, com- 
monly called neurofibromas or fibroneuromas. The true neuromas 
are rather rare in man and almost unknown in domestic animals, 
whereas the false neuromas are comparatively common in man as 
well as in animals. Following neurectomy there are terminal thick- 
enings on the nerve stumps, and although they are called amputation 
neuromas they are simply the regeneration process of the resected 
nerve trunk, but not neoplasms. 
Appearance. — Neurofibromas develop as corded, cylindrical, fusi- 
form, or even nodular thickening of nerve trunks. The perineurium 
undergoes a marked proliferation, forming a grayish structure which 
extends along many of the nerve funiculi in a nerve plexus and giv- 
ing rise to an intertwining plexiform growth. 
Seats. — Ostertag (14), Kitt (11), Morot (13), and others have 
observed these plexiform neurofibromas in the brachial plexus of 
cattle, and the dorsal, intercostal, and sternal nerves as nodular 
3262°— 26 3 
