PALiEOTHERE. 601 



posterior angle of this a second is continued, first downwards, and 

 then along the posterior border of the tooth to the posterior and 

 internal angle where it forms a small eminence or lobe ; a third 

 ridge is continued along the anterior border of the crown to the 

 internal and anterior angle, where it is continued into the summit of a 

 trihedral crucial eminence, forming the anterior half of the inner side 

 of the tooth. A strong conical eminence is developed between the 

 anterior and posterior angles of the inner border of the tooth, and 

 the whole base of the crown is belted by a ridge. As soon as the 

 surface of the crown becomes worn by mastication, and part of the 

 dentine is exposed, it is bounded by two parallel salient lines of 

 enamel, and those upon the outer zigzag ridge form a double 

 crescent, as in m 3 ; if the two inner lobes were equally developed 

 and the intermediate one reduced in size, they would also present 

 their double crescents of enamel, separated by the antero posterior 

 depression from the anterior crescents, and the Ruminant type of 

 molar would be manifested. By the rudimental state of the posterior 

 angular lobes and the varying depth of the crucial fissures, the 

 progress of attrition blends together different eminences and produces 

 a pattern which is very like that of the molars of the Rhinoceros 

 (PI. 135, fig. 5, m 1). The antero-posterior depression, which is the 

 shallowest, is first obliterated, and, with it, the chief resemblance 

 to the Ruminant molar. The transverse fissure is arrested at the 

 point (c) in the hind lobe : a portion of this fissure is sometimes 

 insulated as at e, p 4. As attrition proceeds, both folds are converted 

 into islands of enamel, and, first, the antero-posterior fold c: the 

 islands are finally obliterated before the crown is quite exhausted. 



The first premolar (fig. 5, p 1) is the smallest of the series and 

 has a simple compressed pointed crown, with a strong basal ridge, 

 broadest on the inner side, and a small posterior cusp. The other 

 premolars increase in size until they equal the true molars, from 

 which they scarcely differ in structure. The last true molar has its 

 crown more extended from before backwards, but is contracted 

 posteriorly, that side being the shortest. The first premolar is 

 implanted by three roots : all the others have four roots. 



The crowns of the lower molars are narrower and simpler than 

 those above. The first of the series of seven molars in the lower 



