144 



AGE 'OF THE DOMESTIC ANIMALS. 



roots and the lateral pressure due to the leverage of the crown 

 on its root in the alveolar cavity produce further irritation and 

 prevent proper mastication. The pain on one side frequently 

 confines the grinding entirely to the other. The loss of the 

 lateral motion also prevents the slight fore-and-back play of the 

 arclies of the teeth, and soon the anterior edge of the first molar 

 above and the posterior edge of the last molar below grow into 

 points, which may be very annoying to the animal ; removal of 

 the latter is troublesome to the surgeon. Disease of a molar in one 



Fig. 151. 

 Irregular wearing of upper and lower molars. 



jaw, or its absence from fracture or otherwise, is soon followed 

 by complication in the opposing teeth of the other jaw. Fig. 

 152 shows a fourth molar in the upper jaw with a cavity which 

 was the size of a hen's egg, into which points the fourth inferior 

 molar, wliich, from want of resistance, has become elongated. 

 The presence of a dental cyst probably explains the enlargement 

 of the upper tooth and also the softness of its texture which 

 allowed it to be worn liollow. 



Irregularity and deformity of the molars are the causes of 



