TOOTH-GENESIS IN THE CANTD^. 471 



Of course Osborn is dealiog here with tte human teeth 

 only : otherwise, if he were dealing with the Marsupials as well 

 he could hardly be so satisfied, for in these the Metaconid, 

 instead of developing almost simultaneously with the Paraconid, 

 does not appear until after the Hypo- and Entoconid. 



In the same address, in dealing with the upper jaw, Osborn 

 says so little, that I may quote it all : — " But this, you see, 

 is not exactly the case in the upper molars. Nevertheless, 

 out of eight cusps in the upper and lower molars considered 

 together, six cusps calcify in the order in which they were 

 successively added to the single reptilian cone." Surely this 

 representative of the reptilian cone is tJie important one, and the 

 fact that it does not develop first in any one of these four orders 

 is a point not easily to be explained away. 



Again, it appears to me that Osborn gives undue weight 

 to the lower jaw, almost ignoring the upper, which does not 

 fit in with his views. I would point out that in the Canidge 

 the secondary cusps are better developed in the teeth of the 

 lower jaw than in the corresponding teeth of the upper, both in 

 the milk and permanent dentitions ; and I have already pointed 

 out that the more primitive the teeth the fewer the cusps : con- 

 sequently, it follows that the teeth of the upper jaw retain more 

 of the primitive character than do those of the lower. Hence, if 

 reliance is to be placed on the cusp-development of the teeth in 

 one jaw over those of another, it is the upper jaw which, to my 

 mind, should be selected, and not the lower. 



Trom a consideration of the results obtained by investigation 

 into the embryological history of the cusps, I think it must be 

 admitted that Osborn's conclusions are not borne out, but 

 are, on the contrary, disproved, and this by the very kind of 

 evidence upon which he places reliance. 



There are still other objections which may be urged against 

 the Tritubercular theory. The upholders of this view assume 

 that there has been a rotation of the Paraconid and Metaconid 

 inwards in the lower jaw and outwards in the upper, giving rise 

 to the Tritubercular as opposed to the Triconodon type of tooth. 

 A great objection to this has been put forward by E. S. Grood- 

 rich(5), who points out that there is no evidence whatever of 

 any traces of the beginning of the movement of cusps from the 

 Triconodont to the Tritubercular form. 



