1 1 4 Osteological Description of the 



of their crown is also in a continual state of change j and 

 the naturalist must follow them from the moment when they 

 pierce the gum to that when they fall out of the mouth. 



But it is not always necessary for this purpose to have at 

 one's disposal individuals of all ages. As the fore-teeth 

 appear sooner, they are also sooner worn ; and one may 

 often follow in one jaw all the degrees of detrition pro- 

 ccedinir from the posterior to the anterior teeth. 



ThcJtb'.lowino;, then, are the appearances observed in the 

 teeth of the rhinoceros : — ^The base or neck of the tooth is 

 quadranaular; the interior and posterior side are a little 

 shorter Than the anterior and exterior ; consequently the 

 latter intercept an acute angle, and the others an obtuse. 

 On this base, supposing the side of the root turned down, 

 arise eminences the summit of which is sharp and entirely 

 covered with enamel. As long as the tooth is not wOrn, 

 one of these eminences fits exactly the exterior edge of the 

 tooth, or rather forms it : it has a vertical rib projecting 

 towards the anterior third. 



The second eminence is towards the anterior edge : it is 

 joined to the first at the anterior external angle; then in- 

 clines towards the interior anterior^ but proceeding a little 

 more backu ard than the anterior edoe of the base. 



The third eminence arises from tHe posterior third of the 

 first ; ])roceeds directly inwards, then bifurcates : one of its 

 branches proceeds forwards and the other obliquely back- 

 wai'ds towards the interior posterior. 



These sharp eminences, at a considerable distance from 

 each other at their summits, have broad bases which touch 

 each other. The first cficct of detrition is to wear ofl' the 

 enamel from the summit, and to discover every where a 

 line- of osseous matter bordered with two lines of enamel. 

 In proportion as the detrition increases, and d*;scends to the 

 thick part of the eminences, the lenP'th of the osseous part 

 increases, and that of the hollows between the eminences 

 decreases. When it advances still more, the anterior hook 

 of the third eminence joins itself to the second, and there 

 remains a round hollow towards the middle of the tooth ; 

 a little later another branch of the third eminence unites 

 with the posterior edge of the tooth, and there remains a 

 second hollow behind : these two transverse eminences then 

 tmite at their interior extremity, and leave between them 

 a large oval and oblique hollow in the fore part of the tooth. 

 Ini the last place, when detrition has proceeded to the base 

 t)f the eminences the hollows themselves disappear, and the 

 crown then exhibits a smooth surface of osseous matter sur- 

 rounded by a border of enamel. 



One 



