TEJiTlARY VEKTEBIiATA OF THE FAYIjAI. 
•JO 
whole of the posterior eolunin, tliat is, according to the interpretation here adopted, 
tlie inesostyle, the ])ostero-external and postero-internal cusps. The small inner 
root is imperfectly divided by a vertical g-roove into a larger anterior portion 
sup[)orting that ])art of the anterior main column homologous with the antero- 
internal main cus}), and a smaller posterior portion supporting the portion of the 
cingulum {c.') wdiich in wear unites the inner ends of the main columns. 
The ])reniolars (PI. V. figs. 2, 3) present a sharp contrast to the molars, their 
strikingly diffi'rent a])pearance being due to the presence of an almost flat outer wall 
w'hich show's scarcely any trace of folding. Like the molars they attain a high degree 
of hypsodonty, jiarticularly 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 tow'ards the palate (text-fig. 3, p. 11). The ectoloph 
is flat or at most gently concave from before backw'ards, and it appears to be composed 
of three elements. Of these, one forms the antero-external angle of the tooth and 
is connected with the cingulum on the anterior face of the tooth, so that it may be 
regarded as a parastyle { 2 )S.). The element behind this is a large cusp {r(e.) w'idened 
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 {])&.) forming the 
postero-external angle of the tooth. The anterior face of the tooth is occupied by a 
prominent crest of the cingulum (<?.), w'hich dies away internally, while externally, as 
already mentioned, it is connected with the parastyle. On the inner face of the 
tooth there are tw'o elements {ai. and ^;b), 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 w’ith the ])ostero-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 w'ear-s nr faces of the outer and inner pairs of cusps and the connecting 
transverse ridges (PI. V. fig. 3). 
The three ])osterior premolars have two roots, one anterior the other ])osterior, 
each extending the whole width of the tooth : the division betw'een 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 oidy 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 (Pi. V. fig. 1) and the fwo 
posterior incisors are similar and are also closely crow'ded together. On their inner 
face there is a prominent cingulum enclosing with tlie crown a deep fosette. 
The anterior incisor, judging from its alveolus, is mucli 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 
