526 UNGULATES. 



notch at its posterior and inner angle: the crown is sub-trenchant and 

 tricuspid before it begins to be worn down. A progressive increase 

 of size, and especially of transverse breadth, is combined with a 

 similar form in the first and second true molars {ml & rw 2) ; 

 but the outer notch is deeper, and the two divisions (o, o) more 

 convex, and swollen at their base ; the third molar (m 3) has an 

 additional small hind lobe. The unworn summits of the first and 

 second true niolars are produced into three points in the anterior, 

 and into two points in the posterior lobe. The deep terminations 

 of the folds penetrating the inner side of these semi-cylindrical 

 lobes form crescentic islands of enamel at a certain stage of 

 attrition, and thus typify the Ruminant character of the inferior 

 molars ; but these islands are soon obliterated and the pattern 

 characteristic of the same teeth in the Rhinoceros and some other 

 anisodactyle Pachyderms is produced. In some of the smaller 

 species of Anoplotherium, separated subgenerically under the name 

 of Dichobune, the Ruminant type of grinding surface is more closely 

 adhered to, and is longer retained : in the lower jaw it is produced 

 simply by the crescentic folds of enamel becoming more vertical 

 and sinking into the crown from its summit, instead of penetrating 

 it from the inner side.(l) 



The constituent tissues of the teeth of these ancient Herbivora 

 are the same in number, kind, and microscopic structure as those 

 of existing Ruminants and ordinary Pachyderms. A dense, unvascular, 

 fine-tubed dentine forms the basis ; the crown is defended by a 

 moderately thick coat of fibrous enamel ; and the whole is invested 

 by a cement, which is thickest on the fangs, and at the bottom 

 of the inflected enamel folds of the teeth. The last portion of 

 pulp in the centre of each tooth or tooth-lobe was converted into 

 osteo-dentine, which forms the dark mark on the middle of the 

 much-worn crowns of the teeth of old individuals. The diameter 

 of the dentinal tubes of the canine tooth of the Anoplotherium 



(1) From the close resemblance of these molars to those of the Ruminantia thus produced, 

 it has happened that they have been sometimes referred to that Class : the fossil lower jaw of 

 the species which I have called ' Dichobune cervinum,'' from the eocene tertiary beds in the Isle 

 of Wight was originally described and figured as a species of Ruminant apparently closely aUied 

 to the Genus Moschus. See Geol. Trans. 2nd Ser. Vol. iii, p. 451. 



