600 UNGULATES. 



of their frame best exemplifies the progress of the affinities which 

 the lapse of ages has interrupted. 



The species of Palseotherium which appear to have accompanied 

 the Anoplotheres in the first introduction of hoofed Quadrupeds 

 upon this planet, were characterised by the same complete dental 

 formula, viz : — 



T . 3—3 . 1—1 , 4—4 8—3 . . 



Incisors — ; canmes — ; premolars — - ; molars — : = 44. 



3 — 3 i — 1 4^~4 o™~3 



(PL 135, fig. 4.) But the canines are developed to the proportions 

 which these teeth usually bear as weapons of offence and defence, 

 proportions such as are still manifested by the canines of the Tapir : 

 there is consequently, in the Palaeothere, a vacancy in the series of 

 teeth between the incisors and canine in the upper jaw to receive 

 the crown of the lower canine when the mouth was closed ; and there 

 is a longer vacancy between the canines and the premolars in both 

 jaws. 



The crown of the upper molars is bounded by four unequal 

 sides, the outer side (o o fig. 5) being the longest; in the new- 

 formed and unworn crown this side inclines inwards as it descends ; 

 it is divided by three longitudinal ridges into two concavities, rounded 

 towards the root and terminating in a point at the grinding surface of 

 the tooth : the angles of the base of each projecting triangle rest on 

 the extremities of the salient longitudinal ridges. In the growing 

 molar two vertical sinuous folds of the capsule penetrated the sub- 

 stance of the crown, one (&) entering from within outwards, the other 

 (c, e) crossing it from before backwards. The antero-posterior fold 

 described two curves, parallel with the exterior concavities ; and, 

 entering at the posterior margin, where the valley is widest and 

 deepest, it terminated in a cul-de-sac close to the anterior and outer 

 angle of the tooth, or at a httle distance from the anterior 

 margin : the transverse fold commencing at the inner side of 

 the tooth terminated close to the middle longitudinal ridge on the 

 opposite side, expanding and deepening where it crossed the pre- 

 ceding ridge. Of the salient ridges of enamel left by these folds, and 

 defined by the corresponding valleys, the principal is the zig-zag one 

 which forms the outer boundary of the grinding surface ; from the 



