318 PAL.EOTHEEIUM. 



the tooth, where it expands into a wide and deep depres- 

 sion. The convex inner sides of the lobes c, c, are bor- 

 dered near their base by a ridge. The outer surface of 

 each lobe is gently hollowed out from side to side at d, d, 

 the hollows being bounded by three longitudinal ridges. 

 The posterior lobe is subdivided by a short and wide fis- 

 sure #, which is expanded and deepened at its extremity, 

 like the fissure b. These fissures are formed by folds of 

 the capsule or bag of the formative matrix of the tooth ; 

 and as the capsule supports the organ which forms the 

 enamel, the edges of the folds of enamel so formed, are 

 exposed by the wearing away of the grinding surface of 

 the tooth, and being harder than the dentine or central 

 substance of the tooth, they stand up above it like the 

 exterior border of enamel surrounding the tooth. In 

 specimens of fossil molar teeth of aged animals in which 

 the crown has been much worn, the more shallow beginnings 

 of the enamel folds are worn out, and only the deeper ter- 

 minal depressions remain, forming, as in fig. 113, detached 

 islands of enamel instead of the peninsulas which charac- 

 terise the grinding surface of the molars of younger animals. 

 It is requisite to bear in mind these changes of the pattern 

 of the grinding surface of the complex molars of the Her- 

 bivora in determining the nature of a fossil tooth, lest 

 differences due to age should be mistaken for the dis- 

 tinguishing characters of species or genera. 



I have, as yet, seen no other unequivocal relic of the 

 largest species of true Paleeothere. For the opportunity 

 of examining the fossil figured, I am indebted to the Rev. 

 T. Darwin Fox, M.A. 



