18 



TEETIAEY VBETEBEATA OE THE EATtTM. 



also strongly developed as a prominent crest (c.) in front of the inner half of 

 the anterior column, from which it is separated by a deep fossa, and there is a trace 

 of it on the inner face of the posterior column. On the inner side of the tooth 

 the enamel ceases jnst beneath the cingulum, but on the outer and posterior 

 sides the enamel-covered surface is greatly deepened, so that in a tooth in which 

 the almost unworn posterior column is 11 cm. in height (PL V. figs. 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 column wears to the same pattern : at this stage the tooth appears as 



Text-fig. 6. 



inner 



face. 



innerjace. 



Semi-diagrammatic figure of the upper and lower teeth of the left side of Arginoitlierium andrewsi : 

 A, upper teeth ; B, lower teeth ; C, outer view of last upper molar. 



ffl.c, anterior column of molars ; c, anterior portion of cingulum ; c.', posterior portion 

 of cingulum; ])-'^-' posterior column of molars. About g nat. size. 



an extremely hypsodont bilophodont type. Later the wear on the inner side 

 reaches the level of the cingulum and the surface resulting from the abrasion of the 

 anterior crest of the cingulum joins that of the anterior main column, at first internally 

 only, but afterwards externally also, enclosing with it a deep enamel-lined fossa (PI. V. 

 fig. 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 wall is established and the tooth 



