58 



\Mi:h'fc.\.\ Mi-shiM criDh: lem-lets 



iu<!,s, and indeed tlieic lia\'e been swindlers iiias(|iiei:idiii^ as veterinary 

 dentists, who would gladly "fill" >'()ur horse's teeth for a reasonable 

 considei'ation. These cavities however aic perfect 1\' noiinal, and we have 

 l)recisely the condition here as in the incisors exce|)l thai in the molar 

 the cement is \vv\ much thicker, and the ])i'esence or absence of the 

 ca\ily de|)ends simply upon the thickness of the cement. 



It will be seen that whei'e th(> tooth comes in close contact with its 

 next neiiihboi', the cement is missinji, and indeed, sometimes the con- 

 tinuous line of external enamel is broken (Fijz;. 35). This is due to a 

 sli«»;ht w(»ar on the side of the tooth. Thei'e is a strong tendency to ci-owd 

 towaid each other, thus preventing the foi'cin<2; of food material l)etween 

 them. The slight vibiation when in use, of each tooth in its alveolar 

 socket, ai'foi-ds sufhcicMit weai' to k(H'p \\\o\\\ perfectly fitted together, and 

 also explains the apparent break in the external enamel wall, which we 

 frecjuently se(\ This cr()wdin<2; t()j2;ether, as well as many other features, 

 can best be observed from the side view. On exhil)ition are a numl^er of 

 skulls having- the bone cut away in ordei- to expose to view the full 

 lenjith of the tooth. 



Th(» thi-ee posterior teeth or molars, incUne ver}' considerably to the 

 front, while the other three, the premolars, lean slip;htly toward them 

 (Fijj;. 37), so that when pressure is applied on their grinding surfaces 

 they are foi'ced together like stones in the arch of a building. And as the 

 teeth wear down to a point of smaller diameter, the last molar in extreme 

 old age assumes an almost horizontal position (Fig. 37C). 



The grinders from a lateral view present 

 a most formidable looking dental battery. 

 It gives some idea of their development 

 when w-e find that a full set of premolars 

 and molars, taken from a fair-sized horse of 

 four or fiv(^ years, will weigh about four 

 jiounds, the ])reniolars being a little larger 

 than the molars, a fact which is quite un- 

 usual, as in the great majority of mannnals 

 the ])remolars are very much inferior in size 

 and devel()])ment, as was also the case in the 

 ancestral horse.' 



We see from the lateral view as well as 

 fiom the gi'inding surface, the more highly 

 specialized charact(Ms of the jxM'manent 

 tooth. (\)mi)ai(> the v(My long crowns of 

 Hgure 37.1 with the dcM'iduous molar (Fig. 



Fig. 30. Deciduous molar 



(d. m. *) of colt 11 months 

 old. Natural size, a, crown; 

 h, base of crown: '•, root 



'Sec patjo 1."). 



