THE noh'si' / A />/•;// i^omesthatios 51 



.1 is the pcnuniKMit toolli of n colt two yc.-iis old, hcfoic it li;is I'c- 

 l)l;i('('(l its (Iccitluoiis |)1'(mI(M'i>sso!- or has icM-cixcd ;iiiy wcai', so lliat (he 

 extcMiial (Miamcl is continuous with that of the cul-de-sac oi' iiitciiial 

 onanu^l. The ciMniMit now lin(»s the cul-dc-sac and is he^innin^- to he 

 d(>|)osit(Ml on th(> (^xtciiial enamel. As yet the tooth has no I'oot , hut 

 })resents a wide-()i)en pulp cavity at tlu^ base. 



B is the tooth of a horse about four years old. It has iccently le- 

 placcnl its deciduous ))i(Hlecessoi-, hein*!,- in use only about six months. 

 The folded e(lj2;e of (Miamel is worn thi-()u«»;h, ex})()sin<»; the (l(>ntine beneath, 

 and separatin*2; tlu» (Miamel of the eul-dt^-sac from that of the exterioi-, 

 with \\\v (exception of a vcmt sli<>;ht conncM'tion at the left-hand border. 

 Internal as well as external enamel is covered with cement excei)t on tlu^ 

 wearin<>; surface. The base of the crown is not clearly defined l)ut can 

 rc^ulily 1)(^ located as it coincides with the lower l)or(l(M' of enamel. It 

 will be seen that this point, instead of l)ein^ at the surface of th(^ ^um as 

 in more primitive teeth, is planted about an inch and three-eighths deep, 

 g indicating the gum line. 



C, the tooth of a horse about tw'elve years old, shows a more tri- 

 angular wearing surface, having been worn down a distance of perhaps 

 three-eighths or one-half inch. The cul-de-sac is greatly^ reduced in 

 surface diameter, as well as in depth. The root is fully developed and 

 show^s the nerve foramen (/?) at the point. With the advance of age the 

 wearing surface of the tooth, molar as w^ell as incisor, must necessarily 

 approach the nerve, w'hich would subject it to exposure. This is provided 

 for by the recession of the nerve and a new^ growth of dentine, reducing 

 the nerve or pulp cavity and sometimes in extreme old age completely 

 filling it.^ As the tooth w^ears dow^n this new dentine can be detected in 

 the incisor bj^ a slightly lighter shade in color, and is known among 

 horsemen as the ''dental star." It is indicated in Figure 311) and E. 



In Figure 3 ID, showing the tooth of a horse about seventeen years 

 old, the w^earing surface is still more triangular. The cul-de-sac is almost 

 w^orn aw^a}^; the base of the crown is approaching the gmn line. Not 

 only the crown as in the j^ounger teeth, but the root as well, is becoming 

 thickly covered with cement, so that the base line of the crown is obliter- 

 ated, but can readily be located by sectioning. On the more exposed 

 ridges however, particularly the anterior surface, not shown in the sketch, 

 the cement has been worn through in places b}^ friction of the tongue and 

 lips. 



E shows the condition in extreme old age, this specimen being the 

 tooth of a horse thirtA'-three years old. The cul-de-sac has long since 



iSee specimen No. 132 under "Teeth sectioned to show reduction of pulp cavity" on exhibition 

 in wall case. 



