12 THE DESCENT OF THE PKIMATES 



teeth are most decidedly of a more primitive 

 type, both in the upper and in the knver jaw, 

 than they are in the Lemurs. The crowns of 

 the molars of Tarsius, as also those of Anapto- 

 morphus, which resemble each other most closely, 

 conform to that type and to the initial variation 

 of it which Cope has first designated as the tritu- 

 bercular type. They are tri-cuspid, but the 

 middle cusp is not in one line with the two outer 

 cusps. It lies at a certain distance inward, the 

 three cusps thus enclosing a triangle which is the 

 first indication of what in a more elaborate type 

 of molar teeth will be the grinding surface. Now, 

 in the Lemurs this primitive arrangement is less 

 purely preserved, the true molars being mostly 

 quadri-tubercular. We find it, on the contrary, 

 most distinctly in those fossil precursors of the 

 Tertiary mammals that lived in the Mesozoic 

 period and to which Osborn has given the name 

 of Inscctivora primitiva. Numerous other points 

 of difference by which Tarsius is distinguished 

 from the Lemurs, could be enumerated, many of 

 them having undoubtedly a deeper significance 

 than might appear at first sight. We will, how- 

 ever, allude to them no further, but rather direct 

 our attention to a very remarkable divergence 

 between Tarsius and the Lemurs with which we 



