564 UNGULATES. 



their perennial growth by constantly reproducing the matter to replace 

 the abraded extremities. The direction of the abraded surfaces is 

 in part provided for by the partial disposition of the enamel : in the 

 upper median incisor this is laid upon the fore and outer part of 

 the tooth : in the lateral incisor there is a narrow strip of enamel 

 along the convex side of the tooth. The enamel is soon entirely 

 worn away from the crowns of the lower incisors ; but it is per- 

 sistent in the canines, where it extends to the end of the implanted 

 base ; in the upper canine being laid upon the posterior and outer, 

 and not on the fore part, whilst its position is reversed upon the 

 inferior canine. The grooves and ridges upon the enamel of this 

 tusk are strongly developed : most of them are longitudinal, but the 

 prominent anterior part of the outer surface is traversed by a series 

 of oblique ridges ; and strongly marked transverse grooves and 

 ridges cross the tusk at irregular distances, apparently indicating 

 epochs of the eruption of the tusk. 



The molar series consists of p. J-eJ, m. |e|, = 28.(1) The first 

 premolar has a simple subcompressed conical crown and a single 

 root : it rises early, and at some distance in advance of the second 

 premolar, and is soon shed, the other premolars form a continuous 

 series with the true molars in the existing species ; but in the extinct 

 Hippopotamus 'major ^ whose remains are found in the superficial 

 deposits of this island and on the continent, the second premolar is 

 in advance of the third by an interval equal to its own breadth. This 

 and the fourth premolar retain the simple conical form but with 

 increased size, and are impressed by one or two longitudinal grooves 

 on the outer surface, which when the crown is. much worn give a 

 lobate character to the grinding surface : there is a strong tuberculate 

 ridge on the inner and hinder part of the base of the crow^n, and in 

 the anterior premolars the ridge on the fore and back part of the 

 cone, extending to the summit of the crown is notched or 

 tuberculate near its base. In the premolars of apparently the 

 Hippopotamus minor figured in the work of Scilla 'De Corporibus 



(1) M. Fr. Cuvier assigns ' fausses molaires f, molaires f , to the genus Hippopotamus 

 in the * Dents des Maramiferes' p. 206 ; but the first molar was shed and the last deciduous 

 molar was not shed in the lower jaw of the specimen which he figures and describes, whence 

 the mistake. 



