CHAPTER V. 



SECOND OUTLINE (1897) OF TRITUBERCULAR EVOLUTION IN 

 MAMMALIA. WITH DISCUSSION OF CRITICISMS. 



[Reprinted from an article entitled " Trituberculy : A Review dedicated to the late 

 Professor Cope,'' The American Naturalist, December 1897, pp. 993-1016.] 



THE morphology of the crowns of the mammalian teeth has sprung up 

 practically as a new branch of study since Edward D. Cope and other 

 palaeontologists have demonstrated the unity of derivation of all the com- 

 plex forms from the tritubercular type. The older works and ideas of 

 Cuvier, Owen, Huxley and others are of comparatively little service now, 

 for they treat the teeth of each order of mammals as of so many distinct 

 types, whereas they must now be treated as modifications of one type. 

 This new odontography of the mammalia may be dated from the time 

 when it was recognized that the crowns of the teeth of the Unguiculata 

 and Ungulata, in the comprehensive Linnsean sense, are based upon a 

 common type and are composed of homologous elements of similar origin, 

 as developed by Cope, Osborn, Scott, Schlosser and others. It dates also 

 from the new embryology of the teeth as studied by Leche, Kiikenthal, 

 Taeker, Rose, Woodward [M. R] and others, with the revelations as to 

 primitive form, number, and milk succession. 



But to fully establish the morphological branch in its new era we 

 must first demonstrate the theory of a tritubercular archetype. This has 

 been opposed in one form or other by nearly all English morphologists, 

 namely : Lankester, Forsyth-Major, Newton-Parker, M. R Woodward, E. 

 S. Goodrich, Marion Tims. It has been accepted only by Flower and 

 Lydekker. In Germany it has been accepted by v. Zittel, Schlosser and 

 Riitimeyer ; Schlosser, especially, has made important contributions to the 

 evidence. The theory is accepted somewhat reservedly by the embryo- 

 logists Rose, Leche, Taeker and others, who have attacked rather the 

 homologies of the upper and lower cusps than the theory itself. In 

 France it appears to have made little headway. In America, Scott, 

 Allen, Wortman, Earle and many others are working upon the trituber- 

 cular theory and have made important additions to it. It is difficult 



