312 VETERINARY MEDICINE AND SURGERY. 



appeared even from the corner teeth, but it may remain some time 

 longer. 



Many casual circumstances, nowever, cause a certain degree of devia- 



FlG. 146. 

 The Mark at Eight Years. 



tion from these general rules. The time, which the mark takes to wear 

 out, will vary in different horses according to the hardness or otherwise 

 of the teeth and according to the nature of the food on which the animal 



Fig. 147. 

 The Mark at Nine Years. 



is kept. In grass-fed horses the marks usually remain at least a year and 

 sometimes two years longer than in those fed on hard food. Again in 

 parrot-mouthed horses, that is, where the upper overlaps the lower jaw, 

 the marks may remain for many years. (Fig. 148.) 



On the other hand, some horses, which have a trick of biting the 

 manger, wear down their teeth very rapidly, and therefore lose their 

 marks very early. Horses fed on salt marshes where the sea sand is 

 washed up among the grass, or on sandy plains or meadows, are affected 

 by the increased friction on the teeth caused by the sand. Occasionally 

 a projecting tooth in the upper jaw may cause unusual friction on the 



