AGE, AS INDICATED BY THE TEETH. 421 



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 

 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. 29.) 



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 

 corresponding tooth of the lower jaw, and so may hasten obliteration of 

 the mark. 



Most of these and other causes of irregularity of wear, which might be 

 mentioned, are at once apparent to a careful and accurate observer, and 

 will scarcely prevent his forming a pretty correct opinion of the age. 



The upper incisors, as previously stated, are considerably longer and 

 larger than the lower, and the infundibulum is nearly twice as deep. 

 The marks therefore remain longer than in the lower teeth. We mention 

 this in passing, lest the reader should be misled, if he should by chance 

 refer to the indications given by the upper teeth to corroborate or correct 

 any opinion as to age, about which he may be in doubt from the appear- 

 ance of the lower jaw. 



Occasionally the dentine on the side of the infundibulum may become 

 stained and even black, and in such cases something like a double mark 

 may be observed. 



The mouth taken as a whole is broader at seven years old than at any 

 other period. After this it gradually narrows with age. In this respect 

 the drawings, taken as a consecutive series, are in some degree at fault, 

 as the Author found it impossible to get mouths of the required ages to 

 form a perfect ideal series. For instance, the mouth represented in figure 

 16 (extreme age) obviously has belonged to a very different animal from 

 that shown in the preceding figure. Again, figures 16 and 17 are fair 

 specimens, though very diverse, of what may be expected in extreme age. 



872. Bishop-ing. 



Marks on the incisors are occasionally simulated by means of caustic 

 or the hot iron by low dealers with the view of deceiving the unwary. 



The fraud is readily detected, because though it is easy to make a black 

 mark on the crowns of the teeth, yet it is impossible to restore the wall 

 of pearly enamel, which surrounds the natural mark. (Figs. 19, 190.) 



873. The Fang-hole or Secondary Mark. 



About nine years old, in consequence of the wearing down of the teeth, 

 a slight trace of the fang-hole usually appears in the centre teoth, and 



