THE SKELETON AND ITS JOINTS 369 
Common Opossum (Didelphys virginiana) 9. Osteosarcoma of al- 
veolus, rarefying osteitis deformans of skull, hypertrophy of thyroid, 
acute catarrhal enteritis, acute hyperplasia of spleen. About the middle 
of both lower rami and involving the posterior half of each upper 
maxilla is a uniform elliptical growth apparently emanating from 
alveolus. Teeth not loose, but can be moved in tumor to be described. 
On section a white glistening homogeneous growth is seen apparently 
originating in the body of the alveolus and around the teeth. The shaft 
of bone is soft and easily broken. What remains of marrow is irregu- 
larly injected. In upper jaw there is a distinct porosis of facial bones; 
they and the enclosed sinuses are deeply injected. Lower four ribs on 
both sides show distinct nodulations of pale color along a bluish 
bone. All ribs are very soft and section shows osteoporosis of shaft 
with injected marrow and distinct cartilaginous periosteal bone forma- 
tion. The skull is everywhere soft and the bone is apparently in- 
creased in thickness, rich in blood, but porotic. Rest of skeleton seems 
well calcified. Microscopic section of tumor shows practically the 
same picture. Bone is nowhere normal in amount and proportion but 
the Haversian systems seem properly made, the abnormality consisting 
chiefly of cellular and fibrous growth around larger lamellae, which at 
times is normal in amount but usually much in excess. In places this 
consists wholly of fibroblasts, at others of giant and round cells very 
suggestive of sarcoma; indeed all areas must be called giant-cell sar- 
coma. There is an attempt to lay down osteoid tissue at places par- 
ticularly beneath periosteum. The giant cells are in great numbers 
and some seem osteoclastic. As the lamellae disappear young connective 
tissue seems to take their place but giant cells do not remain numerous 
at such places. Despite its atypical nature it must probably be looked 
upon as an osteosarcoma. The tooth socket is not much involved save 
for hyalinization of root matrix immediately about dentinal zone. 
In another Isabelline Gazelle {Gazella isahella) there 
was a fibro-osteoma localized to one side of the superior 
maxilla (Fig. 48) ; this has been included among the 
tumors, while the above mentioned cases have not been 
so grouped. 
True osteosarcoma seems not to have occurred. One 
tumor was seen upon the wing of a Cuvier's Toucan 
(Rhamphastos cuvieri) which was formerly diagnosed as 
sarcoma, but later examination reveals some giant cells 
in arrangement suggestive of tuberculous osteitis ; since 
this is the only case and not unequivocally a tumor its 
record is hardly warranted. Osteomata of the hard 
variety have been seen on the ribs of a pigeon and a 
