188 



EVOLUTION OF MAMMALIAN MOLAR TEETH 



upgrowth of successive cingula (talons and talonids) it transformed a 

 bilophodont into a trilophodont crown, a trilophodont into a tetralo- 

 phodont, etc. Thus, the plates of the teeth of Elqihas owe their 

 origin to upgrowths of the posterior basal cingulum. 



We have many analogies among other hoofed animals with Probos- 

 cidean molar evolution. Among Suina, Perchcerus has plainly quadri- 

 tubercular upper molars, and shows the origin of a double trefoil 



FKJ. UK). Inferior view of the skull and teeth of Mcerithenum lyonsi, from the Middle Eocene 

 of Egypt. After Andrews. Scale, about i. 



analogous to that seen in Mastodon. The Hippopotamus also shows 

 a double trefoil. Listriodon of the Middle Eocene of Europe exhibits 

 lophodont teeth remarkably similar to those of Dinothcrium. The 

 hindermost molar of the wart-hog (Phacochcerus) parallels the molars of 

 the Proboscidea in the development of complex many-columned teeth 

 from the constant upgrowth of the talon posteriori)'. 



SPECIAL REFERENCES. 



Falconer, H., and Cautlev, P. T., Fauna Antigua Sivalensis, Part I., pp. 1-64, 

 4to, 1846. 



Andrews, C. H., "On the Evolution of the Proboscidea," Fhilos. Trans. Roy. Soc. 

 Ser. B, Vol. 196, pp. 99-118. London, 1903. 



Gau dry, A., Les Enchamements du monde animal dans les temps geologiques 

 Mammiferes tertiaires, 8vo, 1878, pp. 172-191. 



SlKENIA. 



The bilophodont molars of the Sirenia (Fig. 191) do not offer any 

 difficulty to the theory of trituberculy, because of the many other 

 cases in which bilophodonty has evolved from sexi-, quadri-, and 

 trituberculy. 



Considerable evidence has been adduced for the belief that the 



