14 BULLETIN 1449, U. S. DEPARTMENT OF AGRICULTURE 
eburneum, of ivorylike hardness and density; (2) osteoma spongi- 
osum, resembling the structure of spongy bone; (3) osteoma medul- 
losum, composed mostly of marrow, supported and reinforced by 
bone spicules. 
Seats. — The tips of the horns in cattle are often the seat of oste- 
omas. Injuries and inflammation to the damaged part may have 
contributed their share in the formation of horn neoplasms. Large 
and common osteomas may be found arising from the sphenoid, 
ethmoid, or the turbinate bones in cattle and horses. The mandible 
and inferior maxilla are other frequent places, as are any of the bones 
of the head, especially in the region of the orbits. 
Structure. — Osteoma eburneum closely resembles compact bone. 
It is made up of bone lamellae, lacunae, and canaliculi, which are 
generally short and ill defined. Some of the lamellae form in a con- 
centric manner around the Haversian canals ; these are the Haversian 
lamellae. Others unite the Haversian systems: they are the inter- 
stitial or ground-bone lamellae. 
The arrangement of the lamellae in osteoma is like that of normal 
bone — external or circumferential, Haversian or concentric, and 
interstitial or ground lamellae. The Haversian canals are less regu- 
lar and their course is at right angles to the axis of the bone. The 
larger canals may contain marrow. The periphery has a closely ad- 
herent capsule which is identical with the periosteum of bone. 
Osteoma spongiosum has the structure of spongy bone, and the 
Haversian canals are expanded to form marrow spaces and loose 
interlacing meshwork of osseous structure, the interior of the spaces 
being occupied by cell structure identical with red marrow. The 
blood vessels are more numerous than in the preceding variety. . 
Osteoma medullosum is composed principally of marrow and has 
fewer bone spicules than the osteoma spongiosum. The capsule in 
the last two varieties is well developed. 
Combinations. — Osteoma frequently combines with other neo- 
plasms as osteofibroma, osteochondroma, and especially osteosarcoma. 
Degeneration, — Secondary degenerative changes, softening, and ne- 
crosis are not infrequent in the spongy and medullary varieties. 
Nature. — Osteoma is a benign neoplasm, nonmetastatic, and encap- 
sulated. Though usually small, as in the dense variety, the spongy 
variety may reach the size of a football. Osteoma may be single but 
more often it is multiple. When in combination with sarcoma it 
becomes malignant and gives metastasis. 
ODONTOMA 
Odontoma is the name applied to excrescences on teeth. They are 
of bonelike hardness, congenital in origin, and composed of dentine, 
enamel, and pulp tissue. All these tissues are in variable propor- 
tion. Simple odontoma affects a single tooth and is met with in 
cows and horses. It usually surrounds the crown, or more rarely the 
root of a tooth. It is usually hard, rounded in shape, about the size 
of a walnut, but has been known to reach the size of an orange. 
The mixed odontoma is soft, composed to a large extent of fibrous 
tissue, numerous blood vessels, odontoblasts, tooth-papilla structure, 
and rudimentary masses of dentine and enamel mixed in the interior 
and found also as a thin, peripheral crust. The mixed odontoma may 
