ANIMAL DENTISTRY. 185 



pterygoid are located posteriorly, and therefore lift the jaw 

 slightly backward at each contraction. The absence of any 

 muscle with an anterior fixed attachment to antagonize this 

 backward traction is the cause of these universal irregulari- 

 ties. The masseter's influence in that connection is insuf- 

 ficient. 



Treatment — In driving horses the anterior ones wound 

 the mucosa and require filing.' 



PROJECTIONS ON THE SUPERIOR CORNERS. 



(See Fig. 72.) 



At about the age of seven years there appears on the 

 superior corner incisor a sharp enamel point which in most 

 instances will disappear during the three ensuing years. 

 This irregularity is due to a congenital deficiency in the di- 

 mension of the inferior corners. They disappear under the 

 influence cited in the preceding paragraph, i. e., the back- 

 ward traction by the muscles of mastication. 



ACQUIRED ELONGATION OF THE MOLARS. 



Definition — Projections of the molars into vacant cavi- 

 ties on the opposing arcades. 



Etiology — The common cause of elongation of this vari- 

 ety is the loss of a molar by extraction. They occur also 

 from the decayed molar that offers no adequate wearing 

 surface for its opponent. Occasionally in old age the molars 

 become excavated from a defect in texture. 



Symptoms — Defective mastication, rejection of food, ac- 

 cumulation of food beneath the buccinator and tumefaction 

 of the jaw are the signs usually directing the attention to 

 such teeth. Palpation and inspection will reveal a large 

 tuberous projection involving one or two teeth in one ar- 

 cade, and a vacant tooth cavity or a decayed tooth, in the 



