H. F. Osborn — Original Tritiibercular Theory. 321 



Art. XXIX. — PaloBontological Evidence for the Original 

 Tritiibercular Theory; by Henry F. Osborn. (With 

 Plate XXI.) 



There lias been a. strong reaction of late against the original 

 tritiibercular theory so far as it concerns the origin of the 

 upper molar teeth of mammals, by embryologists, comparative 

 anatomists- and palaeontologists. Among the latter, Dr. J. L. 

 Wortman has reached especially strong conclusions, which 

 have been published in this Journal.* 



According to the original theory -of Cope as developed by 

 Osborn, the homologue of the main reptilian cone or protocone 

 is invariably situated on the antero-internal, or lingual side in 

 the upper teeth. 



According to the views of the earlier opponents of the tri- 

 tiibercular theory, the protocone is found on the antero-external 

 side, as in the premolars, and corresponds with the cusps which 

 Osborn called the paracone. According to the views of M. F. 

 Wood ward, f which were based on embryology, the protocone 

 varies in position in different groups of mammals, namely, 

 antero-internal sn certain zalambdodont insectivores (Cen- 

 tetes), and antero-external in Dilambdodonta (Erinaceus), as 

 well as in most other mammals. Similarly Wortman, by anal- 

 ogy with the premolars (this Journal, November, 1903)*, believes 

 that the position of the protocone may have been variable, 

 that is, in some cases internal, in others external. 



The whole point of this very complex question turns on the 

 simple question of evidence whether the main reptilian cone, 

 or protocone, of the ancestors of mammals was found upon the 

 antero-internal side or on the antero-external side of the upper 

 molars. 



The original evidence upon which Osborn supported and 

 developed Cope's theory is that derived from the rare upper 

 molar teeth of the Jurassic mammals. Osborn;}; cited (1) the 

 upper teeth of Triconodon, in which the main cone is central, 

 (2) the upper teeth of Peralestes (British Museum) fig. 2, in 

 which the main cone is internal, (3) the upper teeth of Kur- 



* " In view of the facts above set forth, however, I am more firmly than 

 ever of the opinion, that all such attempts [to name the cusps of the molars 

 in accordance with their supposed homologies, rather than with their rela- 

 tive positions] are foredoomed to failure, and I believe they should be aban- 

 doned as utterly useless and confusing ; that of Professor Osborn, being 

 doubly erroneous, is therefore the most open to objection in this regard." 

 (This Journal, vol. xvi, November, 1903, p. 368.) 



fProc. Zool. Soc, Loud., 1896, pp. 557-594. 



\ On the Structure and Classification of the Mesozoic Mammalia. Jour. 

 Acad. Nat. Sci., Phila. (2), ix, pp. 242-246. 



