TUMORS OF DOMESTIC AXIMALS 13 
structureless, but may at times contain elastic or fibrous tissue. 
Chondromas, like normal cartilage, do not contain any blood vessels 
and derive their nutrition from the perichondrium or the capsule 
surrounding the periphery. For that reason they are subject to 
either retrogressive or progressive metamorphosis. 
Combinations. — Chondroma frequently combines with sarcoma, 
myxoma, osteoma, adenoma, or lipoma, occurring in the mixed neo- 
plasms found in the parotid gland, mammary gland, testicle, and 
ovaries. Of these combinations the chondromyxoma, chondrosar- 
coma, and osteochondroma are more frequent than the adenochon- 
droma and chondrolipoma. 
Degeneration. — Chondromas in domestic animals are very prone 
to undergo incomplete calcification or even ossification. The ground 
substance may be affected by mucoid degeneration with the produc- 
tion of softened foci and liquefaction resulting in the formation of 
cysts, which is less common in animals than in man. 
Nature. — The ordinary chondromas are clinically benign neo- 
plasms which give no metastasis and do not recur after removal. 
Exceptionally, however, metastases may be present even in the or- 
dinary tumor and are always present in combinations of chon- 
droma with sarcoma and in mixed neoplasms, when they become 
malignant, give metastasis, and recur after removal. 
CHORDROMA 
Resembling the structure of chondroma and myxoma, the chor- 
droma may be mentioned; it is a rare, diminutive neoplasm of man 
which is about the size of a pea, occurring usually at the base of the 
skull in the vicinity of the spheno-occipital synchondrosis that cor- 
responds to the upper end of the notochord, of which it is considered 
an embryonal remnant. It has also been described in the sacrum 
and coccyx. In structure it consists of cartilage cells, many of 
which are large and vesicular, and a homogeneous, jellylike, inter- 
stitial substance. It is usually benign when small, but more recently 
a number of cases have been reported in which it grew to a large 
size infiltrating the brain substance and becoming malignant. 
This neoplasm has not been described in the domestic animals. 
OSTEOMA 
Definition. — Osteoma is a neoplasm composed of bone tissue. In 
the domestic animals there are a number of osseous deposits which 
result from injuries or inflammation of the periosteum that are 
osteoid conditions but are not true osteomas. The true osteomas are 
usually small and slow-growing neoplasms attached to the bony 
skeleton. They may occur, however, unattached to bones, as in the 
lung, testicle, parotid gland, mammary gland, ovary, and uterus. 
Osteomatoid conditions, such as small protuberances projecting 
from the surface of the bone, the exostoses, osteophytes, splints, and 
spavin are the result of chronic inflammation and should not be con- 
sidered as osteomas. 
Appearance. — Osteomas may be of various shapes. Usually they 
are nodular, hard, at times lobulated, but always firmly or intimately 
attached to the surrounding tissue. According to the density of the 
caseous elements, three varieties may be distinguished: (1) Osteoma 
