PEOFESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTEALIA. 
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one-half ; in Phascolarctos it forms one-fifth of the molar series, in Tliylacoleo 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 4 ) of Phascolarctos , would not 
be surmised by an uninstructed comparer of the restored 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). 
§ 10. Mandibular Characters of Carnivorous and Herbivorous Marsupials . — A high- 
placed condyle is associated with the rotatory movements of the jaw in herbivorous 
Marsupials (XII. fig. 3) as in herbivorous Placentals. Professor Flower’s restoration 
Fig. 6. 
Mandible of Koala {Phascolarctos fuscus), 
one-half the natural size, and grinding- 
surface of teeth, natural size, from nature. 
Fig. 7. 
Skull of “ Tliylacoleo carnifex, restored,” one-fourth 
natural size (after Flowek, XII. p. 312, fig. 1). 
Fig. 8. 
(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 XII. 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. 
Eight mandibular ramus, mutilated 
behind, from nature, one-fourth natural 
size ( Thylacoleo ). 
T Figured in Plate xi. figs. 1 & 2, Philosophical Transactions, 1859. 
