THE TUMORS OF THE SINUSES. 
259 
lesions. They all are due to a tumor of a similar nature, a like 
origin, an epithelioma which has started in the thickness of the 
maxillary. It is true that all epitheliomas of the face and mouth 
do not start at the same point. It is probable that some begin 
on the buccal membrane or that of the sinuses; those of the 
latter are less frequent in horses. Those which are most ob¬ 
served in these regions have the maxillary bone for starting 
point and are no doubt developed at the expense of the epithe¬ 
lial centres loose in the bones, and rising from the dental struc¬ 
tures. At a given time, under the influence of causes, still un¬ 
known, the cells which constitute these centres proliferate 
abnormally and make in the bone a cavity, which gradually 
opens either in the mouth, in the sinuses, most commonly in 
both, the diseased process invades the bone, destroys the walls 
of those cavities as well as the dental alveola. The tumors are 
called terebrciting epithelioma of the maxillary. Kven in the 
cases where the disease is observed early, at the moment where 
the buccal mucous membrane ulcerates, for instance, already 
the maxillary has undergone an extensive destruction through 
its structure and alveolar borders, and yet but little deformity 
of the face exists. 
Be careful of not basing yonr prognosis of the tumors of the 
region of the face from the size of the swelling or the bulging of 
the bony plate. While these epitheliomas of the maxillary , 
scarcely visible , are of the most severe nature , benignant growths , 
covered by the mucous membrane of the sinuses may push against 
the external table of these cavities , thin it out , raise it and per¬ 
forate it , right through the skin , and yet these last benignant 
tumors may be successfully operated upon. The animal is anaes¬ 
thetized, the sinuses freely opened—most ordinarily both max¬ 
illary —and at one or several seatings, the neoplasm is removed, 
the haemorrhage being controlled by plugging or with the 
cautery. With malignant tumors, such operations are not to be 
performed in our surgery. 
I will now resume the practical indications of my remarks : 
Tumors developed on the mucous membrane of the sinuses 
