56 



MAMMALIAN DENTITION 



the highest. In Menacodon the two smaller cones lie somewhat 

 on the internal or lingual aspect of the larger middle one, 

 Spalacotherium presents the two lesser cones adjoining at their 

 bases on the inner aspect of the larger middle cusp, their tips 

 being directed respectively forward and backward. In all 



Dr;jW, A/ wfy 





Fig. 14. — Jaws of Jurassic Triconodonts. (All after Osborn. — Menacodon and the 

 upper figure of Triconodon originally after Marsh. Enlarged.) 



A. Mesial aspect, Triconodon, America. 



B. Mesial and C. lateral aspects, Menacodon, America. 



D. Mesial aspect, Spalacotherium, America. 



E. Mesial aspect, Triconodon, England. 



these mandibles the molar teeth show a strong internal ridge 

 or cingulum. 



The most generalized of all the Triconodonts is Amphilestes 

 with the dental formula: 



*4 



P-,M- r 



which is identical with that of the Cynodonts previously men- 

 tioned. The premolars in this group as in the Cynodonts 

 steadily increase in size from before backward to culminate 



