TEETH OF DIPHYODONTS. 293 



lower jaw, inward. The false and true molars, like the incisors, 

 have persistent pulps, and are, consequently, devoid of true fangs, 

 in which respect the Wombat differs from all other Marsupials, 

 and resembles the extinct Toxodon, the dcntigerous Bruta, and 

 herbivorous Rodentia. 



A retrospect of the modifications of marsupial dentition shows 

 them to be divisible into two classes : one 'polyprotodont,' or cha- 

 racterised by several pairs of mandibular incisors ; the other ( di- 

 protodont,' or by a single pair : these are large, more or less 

 procumbent, and ever-growing; the incisors of the first group 

 are small, and of the usual limited growth. The polyprotodont 

 type prevails in the American genera: the diprotodont obtains 

 in the majority of the Australasian marsupials, and is associated 

 usually with vegetarian or promiscuous diet. There did exist, 

 however, coeval with Diprotodon, Nototherium, &c, in a ter- 

 tiary age in Australia, a carnivorous marsupial equalling the 

 Lion in size, with the di- 



233 



protodont type of dentition 

 adaptively modified for prey- 

 ing on the huger contem- 

 poraneous Herbivora. 



The pair of incisors in the 

 lower jaw, fig. 233, i, and 

 their homotypes above, i l, 

 were ' canines ' in size and 

 shape : a single tooth of the 

 molar series on each side of 

 both jaws, ib. p 4, was concomitantly modified to act as a { sec- 

 torial ' or flesh-cutting tooth ; the crown being narrow or 

 ( compressed,' long antero-posteriorly, with the sides marked by 

 vertical folds or grooves, and converging to a rather oblique 

 cutting edge, that of the upper blade playing on the outside of the 

 lower one. These e sectorials ' were larger than in the Lion or 

 Tiger, and were even more ( carnassial ' as wanting the i tubercle,' 

 and consisting wholly of the i blade.' Behind the upper sectorial 

 is one small tubercular, m i, of the relative proportion of that 

 in Felis : the lower sectorial is followed by two small teeth with 

 subtuberculate crowns, m i, m 2. The teeth between the carnas- 

 sials and laniary incisors are too small for definite use. So far 

 as present fossils show, the dentition of Thylacoleo was : — 



.3.3 1.1 2.2 1.1 

 l Ll ;C O0^2T2 ;7n 2^ =24 - 



The chief business of the teeth was delegated to the tusks and 



Dentition of Thylacoleo. 



