CHANGES IN THE FORM OF THE TEETH FROM WEAR 



399 



tral cavity being surrounded by a continuous line of worn surface. In 

 the central incisors the central cavity is extremely shallow. 



With the changes above described, the evidence afforded during per- 

 manent dentition is completed. 



CHANGES IN THE FOEM OF THE TEETH FEOM AVEAR 



It is customary in examining the mouth of the horse, after the animal 

 has reached the age of five years, to devote special and sometimes exclusive 

 attention to the state of the 

 corner incisors. In cases, how- 

 ever, where an exact opinion is 

 important, the state of the other 

 incisor teeth deserves considera- 

 tion. 



Between five and six years 

 the anterior edge of the corner 

 tooth necessarily undergoes 

 wear, which finally extends 

 along the whole front of the 

 tooth, so that at the completion 

 of the sixth year the incisor 

 has lost its shell-like character; 

 the posterior edge, however, still 

 retains its rounded appearance. 

 These characters are shown in 

 the next illustration (fig. 614). 



At seven years of age the 

 whole of the incisor teeth have assumed a more solid character, and 

 it will be seen at once that they are in some degree approaching the 

 triangular form which is the result of the combined eff"ects of the wear 

 taking place at the upper part, while the teeth are constantly growing 

 from below. 



The central incisors in the seven-year-old horse have their lateral out- 

 lines considerably elongated as compared with the same teeth at six years 

 old. This change is less marked in the lateral and corner teeth. The 

 latter, however, have their tables fully formed. A line of wear, narrower 

 at the posterior than at the anterior edge, encircles the central cavity as 

 shown in the next figure (fig. 615). 



At eight years old the triangular form of the incisors is still more 

 marked. The central enamel in the central teeth corresponds in its tri- 



Fig. 614. — Incisors of Horse at six years 



