IS 
TETITIAIIY VEETEBEATA OF THE FATOM. 
also stronjrly dovc'lojK'd as a prominent crest (c.) in front of the inner half of 
the anterior eolnnin, from which it is sej)arated by a deej) fossa, and there is a trace 
of it on the inner face of the posterior column. On the inner side of the tooth 
tlu' enamel ceases just beneath the cingulum, but on the outer and posterior 
sides the enanud-covercd surface is greatly deepened, so that in a tooth in which 
tlu' almost unworn posterior column is 11 cm. in height (PI. V. tigs. 6 A, 6 b) the 
enamel-covered portion of the crown is only about 3 cm. deep on the inner side, 
while on the outer it is some 8 cm. in depth, and the posterior face of the posterior 
column is covered from base to crown (11 cm.). Wear commences at the summit of the 
anterior column, giving rise to a transversely elongated surface. Next the summit 
of the posterior colunm wears to the same pattern : at this stage the tooth appears as 
Text-fig. 6. 
Semi-diagrammatic figure of the upijer and lower teeth of the left side of Arsinoltherimn andrewsi : 
A, upper teeth ; B, low er teeth ; C, outer view of la.st upper molar. 
a.c., anterior column of molars ; c., anterior portion of cingulum ; c.', posterior portion 
of cingulum; posterior column of molars. About j nat. size. 
an extremely hypsodont bilophodont type. Later the wear on the inner side 
reaches the level of the cingulum and the surftice resulting from the abrasion of the 
anterior crest of the cingulum joins that of the anterior main column, at hrst internally 
only, but afterwards externally also, enclosing with it a deep enamel-lined fossa (PI. Ah 
hg. 7). At the same time the posterior portion of the cingulum comes into wear : 
its surface is at first continuous with that of the posterior column, but later with the 
anterior also, so that at this stage a continuous inner Avail is established and the tooth 
