12 BULLETIN 1449, U. S. DEPARTMENT OF AGRICULTURE 
in nature, are intermingled with the cells. Between the cells and 
fibers is the gelatinous, homogeneous, interstitial ground substance. 
A few blood vessels and lymph vessels are invariably present. 
Combinations. — Myxoma is sometimes combined with fibroma, lip- 
oma, and sarcoma, but most authorities are inclined to regard these 
combinations more as a process of mucous degeneration of the above- 
mentioned neoplasms rather than a combination with the myxoma. 
Degeneration. — Myxomas frequently become edematous or under- 
go degeneration which is followed by the formation of a cyst. 
Nature. — Clinically, myxomas are benign, nonmetastatic, slow- 
growing neoplasms. Their capsule is more delicate than in the 
fibroma of the lipoma and is often almost entirely absent when the 
myxoma assumes the lobulated form. At times, however, myxomas 
may grow rapidly, and the cell processes become absorbed, the inter- 
stitial substance is reduced in quantity, whereb}^ the cells are closer 
together and the neoplasm develops a malignant tendency. 
CHONDROMA 
Definition. — Chondroma is a neoplasm composed of cartilage and 
a variable amount of fibrous connective tissue, which forms a capsule 
on the periphery and penetrates into the interior of the neoplasm. 
Chondromas may be found in all domestic animals, especially in 
sheep, cattle, hogs, and horses, also rather commonly in dogs and do- 
mestic fowls. 
Appearance. — Chondromas are nodular, lobulated, or rounded in 
shape, white or whitish gray, translucent when the hyaline cartilage 
predominates, and of a bluish-white tint on section. The color may 
be yellowish when elastic tissue predominates. 
Seats. — Two distinct forms may be considered: (1) Chondroma 
proper or enchondroma, and (2) cartilaginous outgrowths or ecchon- 
droma. The first, originating in noncartilaginous tissue, is the more 
usual form and is associated with the osseous system, starting from 
the periosteum and less frequently in the bone marrow. The sternum 
and ribs are frequently subject to injuries in domestic animals and 
are common seats of chondroma growing from the periosteum. The 
maxillary bone and the long bones are less frequently involved in 
the process. More rarely chondromas are found in the thyroid, paro- 
tid, and mammary glands, the testicle, and the ovary. In these lo- 
calities chondromas must be the result of misplaced embryonic cell 
rests, congenital in origin, and are frequently combined with other 
neoplasms. 
Ecchondromas or cartilaginous outgrowths originate from the 
perichondrium of the laryngeal, tracheal, and bronchial cartilages of 
the lung. 
Structure. — Under the microscope chondromas usually resemble 
hyaline cartilage, less frequently elastic cartilage or fibrocartilage. 
The cells in chondromas are more irregular in shape and size, not- 
only in different growths, but also in different parts of the same 
neoplasm. Several cells or groups of cells may be present in a 
lacuna and the capsule is generally absent. Some chondromas are 
very cellular, others are poor in cells. The smaller cells are always 
peripheral and the larger cells are central. Between the cells is 
the matrix, wdiich is usually hyaline and homogenous or apparently 
