20 TEETIAET VEETEBEATA OF THE EAYtTM. 



whole of the posterior column, that is, according to the interpretation here adopted, 

 the mesostyle, the postero-external and postero-internal cusps. The small inner 

 root is imperfectly divided by a vertical groove into a larger anterior portion 

 supporting that part of the anterior main column homologous with the antero- 

 internal main cusp, and a smaller posterior portion supporting the portion of the 

 cingulum (cJ) which in wear unites the inner ends of the main columns. 



The premolars (PL V. tigs. 2, 3) present a sharp contrast to the molars, their 

 strikingly different appearance being due to the presence of an almost flat outer wall 

 which shows scarcely any trace of folding. Like the molars they attain a high degree 

 of hypsodonty, particularly on their outer side, where the enamel-covered portion of 

 the crown is almost four times as high as on the inner side (PI. V. fig. 3 a): in 

 consequence of this, as in the case of the molars, these teeth are strongly curved, 

 the concave face being turned towards the palate (text-fig. 3, p. 11). The ectoloph 

 is flat or at most gently concave from before backwards, and it appears to be composed 

 of three elements. Of these, one forms the antero-external angle of the tooth and 

 is connected \vith the cingulum on the anterior face of the tooth, so that it may be 

 regarded as a parastyle (jos.). The element behind this is a large cusp (ae.) widened 

 out transversely as it wears down, so that eventually it forms a junction with the cusp 

 (ai.) internal to it. Behind this main outer cusp is a smaller one (pe.) forming the 

 postero-external angle of the tooth. The anterior face of the tooth is occupied by a 

 prominent crest of the cingulum (c), which dies away internally, while externally, as 

 already mentioned, it is connected with the parastyle. On the inner face of the 

 tooth there are two elements {ai. and pi-), the anterior of which is the larger. This 

 becomes connected with the antero-external cusp, forming a transverse crest, and at 

 the same time it is united by a ridge with the postero-internal cusp. In still later 

 stages of wear this postero-internal cusp becomes united with the postero-external, 

 so that finally the centre of the tooth is occupied by an enamel-lined pit enclosed by 

 the continuous wear-surfaces of the outer and inner pairs of cusps and the connecting 

 transverse ridges (PI. V. fig. 3). 



The three posterior premolars have two roots, one anterior the other posterior, 

 each extending the whole width of the tooth : the division between the roots is much 

 deeper on the inner than on the outer side (PI, V. fig. 3 a). 



The anterior premolar is simpler than the others, having only one root. It is 

 closely crowded between the second premolar and the canine, which it much resembles, 

 being a simple curved columnar tooth. The canine (PL V. fig. 1) and the two 

 posterior incisors are similar and are also closely crowded together. On their inner 

 face there is a prominent cingulum enclosing with the crown a deep fosette. 



The anterior incisor, judging from its alveolus, is much larger than the others. 

 In no specimen has this tooth been found in situ, but an isolated example almost 

 certainly referable to this position has a curved and pointed crown with a shelf-like 



