114 



EVOLUTION OF MAMMALIAN MOLAR TEETH 



of two triangles, the hinder one being formed from the enlarged talonid, 

 the apices of these triangles being external and fitting in the spaces 

 between successive outer triangles of the upper molars.* 



rne. 



Fin. 61. Dentition of the Marsupial Mole, Notoryctes typlilops. X T . After E. C. Stirling. 



Thus, in conclusion, the various Marsupials afford the most con- 

 vincing evidence of tritubercular origin. It is only necessary to 



understand the intermediate stages and to 

 compare even the most highly specialized 

 teeth with analogous types among the Pla- 

 centals, to be convinced of the universal 

 tritubercular derivation. Howes (Sept. -Brit. 

 Assoc., Belfast, ]902) declared he could not 

 conceive the derivation of the Diprotodon 

 molar from the tritubercular type, but com- 

 parison of these teeth with those of Macropus 

 and the stages leading to the Macropus type, 

 FIG. t;-2. First upper molar of together with the still stronger but more 



NotorycUs lHf>ldp*, upper figure, m 



crown view -, lower figure, anterior indirect evidence anoi'ded by the Jrlacentals 1 



view. XT- After E. C. Stirling. T 7-, 7 * -\ -n ij.' 



indicates that the Diprotodon molar will ulti- 

 mately be found to be of tritubercular origin. 



SPECIAL REFERENCES. 



Dentition of Marsupials (figures and descriptions). 



Owen, Eichard, Odontography, 1840-1845. 



Tomes, C. S., A Manual of Dental Anatomy, 1898. 



Bronn, H. G., Klassen und Ordnungen des Thier-reichs, Bd. I., pp. 169-177. 



Schlosser, M., Die Affen . . . Marsupialier . . . des Europaischen Tertitirs, etc., 

 Wien, 1887-90. 



De Blainville, H. M. D., Osteographie des Mammiferes, Tome III., Paris, 1839-1864. 



Bensley, B. A., " Oh the Evolution of the Australian Marsupialia ; with Remarks 

 on the Relationships of the Marsupials in general." Trans. Linn. Soc., 28 Ser., 

 Vol. IX., Pt. 3, Dec. 1903, pp. 83-217. 



*[As in other mammals the protocone opposes the talonid of the preceding lower molar, 

 the hypocone opposes the trigonid of the corresponding lower molar. ED.] 



1 Compare the similar lophodont molars of the Tapir with the lophodont to quadrituber- 

 cular molars of Syxtemodon (Fig. 172). 



