ON THE BONES OF THE RHINOCEROS* 421 



fig. 3*. The base or neck of the tooth is quadrangular; the internal 

 side, e c, and the posterior, e b, are a little shorter than the anterior, 

 c a, and than the exterior, a b ; consequently the latter intercept an 

 acute angle, a, and the others an obtuse angle, e. 



On this base (supposing the side of the root below), there are 

 raised eminences, the summit of which is cutting (trenchant) and en- 

 tirely covered with enamel, so long as the tooth is not worn down. 



One of these eminences, a b, follows exactly the external edge of 

 the tooth, or rather the form : it has a vertical side, blunt and a little 

 prominent towards the anterior third (in d). 



The second eminence, a c, is towards the anterior edge ; it is joined 

 to the first at the external anterior angle ; then it is directed towards the 

 internal anterior, but going a little farther back than the anterior edge 

 of the base. 



The third eminence, b e, sets out from the posterior third of the first, 

 goes first directly inwards, then is bifurcated ; one of its branches, f, 

 forms a root, which goes forward ; the other, e, goes obliquely back- 

 wards towards the posterior internal angle. 



Between them there is intercepted a sort of oblique hollow, broader 

 at its lower part, and which opens by a kind of throat at the internal 

 edge of the tooth. 



In fine, at the posterior edge of the tooth, which is also that of this 

 third eminence, there is a considerable slope, g. 



These eminences, at first cutting, and considerably distant from each 

 other at their summits, as they may be seen, for example, plate 43, 

 fig. 1 , A and B, have widened bases, which touch. The first effect of 

 detrition is to wear the enamel of the summit, and to uncover every 

 where a line of osseous substance edged by two lines of enamel. 

 According as detrition increases, and descends to the thick part of the 

 eminences, the breadth of the osseous part increases, and that of the 

 hollows between the eminences diminishes, as in B, fig. 3, plate 40. 

 When it advances still more, the anterior hook of the third eminence 

 is joined to the second, and from the hollow intercepted by the two 

 eminences, there is separated a round cavity towards the middle of 

 the tooth, as in C, ib. ; soon after, the other branch of the third eminence 

 is united to the posterior edge of the tooth ; and what was but a slope, 

 g, becomes a cavity hollowed out on every side ; there is then a second 

 cavity behind, as in D and E, ib. ; then these two transverse eminences 

 are united at their inner extremity, and the depression which they in- 

 tercepted is changed into a great excavated hollow, of an irregularly 

 oval figure, and placed obliquely before the tooth again, as at D. It 

 is even sometimes divided into two, when it is worn down to the 

 bottom, as at E and F. Finally, when detrition has gone as far as the 

 base of the eminences, even the hollows disappear, and the crown 

 merely presents a surface of osseous substance surrounded by an edge 

 of enamel, as at G. 



* Figs. 3 and 4 of plate 43 are taken from an old animal. Fig. 1 , plate 43, though 

 belonging to the Java species, being from a younger animal, gives an idea of what 

 these teeth are before they are so much used . 



VOL. I. MM 



