TYPES AND MARKET CLASSES OF LIVE STOCK 371 



the surface of the milk teeth is smooth. At 3% to 4 years, 

 the intermediate pair of permanent incisors appears in each 

 jaw. At 4 ^2 to ^ years, the corner pair of milk teeth above 

 and below are displaced by permanents, and the horse may 

 be said to have reached maturity. 



After five years the age is not so easily determined, nor 

 are the indications so accurate. We rely mostly upon changes 

 in appearance shown by the wearing surfaces of the teeth to 

 tell us the age beyond five years. The wearing surface of new 

 permanent teeth has a long, narrow cup or depression running 

 across it transversely. The rims of these cups disappear through 

 wear, leaving two distinct rings of enamel, one around the margin 

 of the tooth, and the other around the cup. With wear, the 

 cup becomes smaller, more oval or rounding in shape, and more 

 shallow, until it is finally worn almost completely away. Con- 

 tinued wear exposes the tip of the pulp canal or cavity in the 

 center of the tooth, and the exposed tip of this canal appears 

 between what is left of the cup and the front of the tooth. The 

 exposed pulp cavity is called the dental star. 



At six years, the middle pair in the lower jaw are usually 

 worn level and the wearing surface tends to become oval in form. 

 The central ring of enamel is plainly evident, but is smaller 

 than at five years, indicating considerable wear. The lower 

 corner teeth, which at five years showed little or no wear, now 

 usually show wear, the edge surrounding the cup being much 

 less sharp and shell-like. The canine teeth, which first ap- 

 peared at four years are now completely out. At seven years, 

 the lower intermediates are also levelled on the wearing surface 

 and the ring of central enamel becomes wider from before back- 

 ward, and shorter from side to side. A hook or swallow tail 

 is often present on the upper corner teeth because they are 

 broader than the lower corners and do not wear down evenly. 

 At eight years, all the lower teeth are levelled and the dental 

 star appears upon the center and intermediate pairs, showing 

 between the front border of the tooth and the front border of 

 the central enamel. 



At nine years, the hook or swallow tail on the upper corners 

 has often disappeared. The lower centers are round; their 

 central enamel has a triangular form; and their dental star is 

 narrower and more distinct. The center pair of the upper jaw 

 are usually leveled. At ten years, the changes previously men- 

 tioned become more marked, and the upper intermediates are 



