153 



one-half ; in Phascolarctos it forms one-fifth of the molar series, in Thylacoleo it forms 

 two-thirds of that series ; these proportions are masked in the foreshortened view, fig. 5. 



The premolar in the upper jaw of the Koala (p 4, fig. 6) presents a flat surface, 

 with a breadth of crown two-thirds of the length, the surface being slightly raised by 

 a border of thick enamel at the periphery, and by a plicate island of enamel in the 

 middle. It is a true pounder of vegetable substances, with the structure of a type- 

 grinder of an herbivore. Such contrast in proportions, structure, form, and function 

 with p 4 in Tliylacoleo*, as is presented by the tooth (p *) of Phascolarctos, would not 

 be surmised by an uninstructed comparer of the imaginary restoration of Tliylacoleo 

 (fig. 4, copied from XII. fig. 2) with the corresponding view of its alleged herbivorous 

 analogue and ally (fig. 5, copied from ib. fig. 4). 



Mandibular Characters of Carnivorous and Herbivorous Marsupials. — A high- 

 placed condyle is associated with the rotatory movements of the jaw in herbivorous 

 Marsupials (fig. 6, b) as in herbivorous Placentals. Professor Flower's restoration 



Fier. 6. 



Mandible of Koala (Phascolarctos fttscus), 

 one-half the natural size, and grinding- 

 surface of teeth, natural size, from nature. 



Skull of " Thylacoleo camifex, restored," one-fourth 

 natural size (after Flower, XII. p. 312, fig. 1). 



(fig. 7, copied from XII. p. 312, fig. 1) gives a similar position to the mandibular con- 

 dyle (b) in Thylacoleo, and the angle (a) is there indicated after the pattern of the lower 



jaw of the Koala (fig. 6, a). 



The first fossil mandible of Thylacoleo which 

 permits a deduction to be made of the relative 

 position of the parts in question (Plate VIII. figs. 1 

 & 2, and Cut, fig. 8), demonstrates the fallacy of 

 the restoration in fig. 7, and shows a structure har- 

 monizing with powerful vertical movements of the 

 mandible, not with the horizontal grinding required 

 for the comminution, and mixing with abundant 

 saliva, of vegetable matters. 



* Figured in Plate XI. figs. 1 & 2, Philosophical Transactions, 1859 



Fig. 8. 



Eight mandibular ramus, mutilated 

 behind, from nature, one-fourth natural 

 size (Thylacoleo). 



