THE HORSE 



349 



sors, then the second incisors, and lastly the third 

 incisors. The three pairs succeed one another at 

 intervals of about a year. I will add that the milk 

 teeth are whiter and narrower than the others. You 

 already see that by examining the incisors and 

 noting whether they are first or second teeth we can 

 tell the age of a young horse ; but there are other dis- 

 tinctive marks which we must now learn. 



"Here is a picture of the longitudinal section of 

 a horse's incisor. In the lower part, or root, of the 

 tooth is a cavity occupied by the 

 nerve which gives sensitiveness to 

 the tooth and which carries to it, in 

 the blood, the materials for its 

 growth and maintenance. The up- 

 per part, or crown, likewise con- 

 tains a depression, which is called 

 the pit or cavity of the crown, and 

 is filled with blackish matter. A 

 layer of enamel covers the outside 

 of the tooth, folds over the crown, 

 and extends into the cavity, the 

 walls of which it lines. The rest 

 of the tooth is composed of 

 ivory. 



1 ' From this structure you will see that the enamel, 

 continuing uninterruptedly from ,the outside to the 

 inside, forms a sharp ridge on the edges of the cor- 

 onal cavity. But this condition does not last long 

 and is found only in incisors of recent formation. 

 In fact, by the grinding of the teeth one against an- 



Longitudinal Section 

 of a Horse's Incisor 



