28 CLINICAL VETERINARY MEDICINE AND SURGERY. 



painful, but moveable under the skin. The mouth was offensive. 

 On examining the buccal cavity, considerable destruction of mucous 

 membrane was noted on the left, and the gum on either side of the 

 row of molars was covered with vegetations. By using the mouth-gag, 

 the second, third, and fifth molars were found to be loose and implanted 

 in a soft tissue. They were surrounded with decomposing food. The 

 fourth molar had fallen out, its place being occupied by fungating new 

 tissue. In order to make a more complete examination the animal 

 was cast and chloroformed. The face was trephined at three points 

 around the centre of the tumour. The large opening thus made 

 showed the greater part of the maxilla to be destroyed, and exposed 

 the roots of the molars, whose bony alveoli had disappeared. The 

 second and fourth molars were removed. 



Diagnosis was easy. The symptoms were due to a tumour, which 

 had invaded the greater part of the superior maxillary bone, had filled 

 the sinuses, and had perforated the bony palate. Microscopic 

 examination showed it to be another case of epithelioma of the 

 pavement epithelium type. 



The animal was slaughtered. No secondary growths could be 

 detected in the viscera. The superior maxilla was almost completely 

 destroyed. The first molar was still fairly firm, but the fifth and sixth 

 yielded to gentle traction. The new growth hardly projected above 

 the level of the palate, which, however, was invaded throughout the 

 entire left side, from its posterior border to a point level with the first 

 molar. 



You see that these three cases are almost similar, the only 

 differences being the position and extent of the lesions. In all three 

 the tumours are similar in nature and origin — are, in fact, epithe- 

 liomata affecting deep-seated portions of the maxilla. Epithelial 

 tumours originating in the mucous membrane of the mouth, nose, or 

 sinuses, certainly occur, but are rare in the horse. Those most 

 commonly seen in this region usually start from the maxilla. They 

 undoubtedly develop from, and at the expense of, paradental epi- 

 thelial debris, according to M. Malassez's theory in the case of similar 

 tumours in man. Under the influence of hitherto unrecognised 

 stimuli, the cells forming these small tracts of tissue may at any 

 moment commence to proliferate, and may form in the depths of the 

 bone a tumour which afterwards extends towards the mouth or 

 sinuses, most frequently towards both simultaneously. Little by 

 little the cancer destroys the walls of these cavities and the alveoli of 

 the teeth. Sometimes it excavates in the bone a large cavity, lined 



