216 THE HORSE IN HEALTH AND DISEASE 



to infection. Normally the gums hermetically seal the alveolus 

 from external influences. Treatment consists in early extraction. 



A tooth fistula is an opening near the root of a tooth through 

 which a continuous, foul-smelling, discharge of pus escapes. The 

 diseased tooth must be completely removed before the fistula can 

 be cured. It oftenest occurs in young horses and is commoner in 

 the lower than the upper jaw. 



Irregularities of wear in the teeth occur surprisingly often. 

 They are due to unequal hardness of opposing teeth, or to congeni- 

 tal deformities, like a narrow upper or lower jaw. The first condi- 

 tion leads to the formation of sharp, enamel points that may injure 

 the tongue or cheeks if not removed. Sometimes a wave-formed 

 mouth results, or that closely aUied irregularity, the step-formed 

 mouth. Parrot-mouth, or receding jaw, and shear- or scissor- 

 formed mouth (Fig. 63) are congenital anomalies in which the teeth 

 of the two arcades do not wear on each other. 



