50 Mr. Owen on the Thylacotherium, 



A similar impression would be made by the outer side of the coronoid process of 

 the Mole's jaw, but not by that of any known reptile or fish. 



In the Opossum's jaw it will be likewise perceived that a depression is con- 

 tinued forwards and slightly downwards from the condyle of the jaw to the 

 foramen of the dental artery and nerve : in the fossil a corresponding depression 

 of the jaw has left a convex elevation of the matrix, leading likewise from the 

 condyle to the dental foramen ; but this foramen, in the Tliylacotherium, is 

 situated relatively more forwards than in the Didelphys. 



What therefore might at first sight seem to be an imperfection in the present 

 fossil, affords in reality an additional clue for tracing out its true affinities. The 

 fossil resembles the Didelphys in the breadth, the height, and the direction of the 

 coronoid process ; but, among the placental Insectivores, the Gymnurus Rafflesii 

 sufficiently resembles in these particulars the present Stonesfield fossils, to prevent 

 undue stress being laid upon the modifications of the coronoid process as indica- 

 tive of their marsupial affinities. 



The simple structure of the jaw of the Thylacothere, its convex prominent 

 condyle, and the process continued backwards from the angle of the jaw, have 

 been adduced by M. Valenciennes as estabhshing the truth of Cuvier's opinion 

 of the nature of that extinct animal ; and we have seen that all the fossils hitherto 

 discovered justify such support. But these anatomical facts only go to prove the 

 mammiferous and carnivorous, and not the marsupial character of the Thyla- 

 cotherium : there is however a constant modification of the angle of the jaw, 

 recognised by Cuvier*" as peculiar to the family of Opossums {Pedimanes), and 

 which I have found to characterize, not only that family, but all the marsupials 

 hitherto discovered, and to distinguish them from their nearest congeners in the 

 placental series : this character has not been taken into consideration in the 

 inquiry into the nature of the present fossils by any of the able anatomists who 

 have written respecting them, although, if co-existing with a convex condyle, it 

 would be strong evidence of the marsupial nature of a fossil jaw, even if all the 

 teeth were wanting. 



In the carnivorous Marsupials, as the Thylacine, for instance, the lower max- 

 illary bone resembles, in many respects, that of the corresponding species in the 

 placental series, as the Dog : a similar transverse condyle is placed low down near 

 the angle of the jaw ; a broad and strong coronoid process rises high above the 

 condyle, and is slightly curved backwards ; there is the same well-marked depres- 

 sion on the exterior of the ascending ramus for the firm implantation of the tem- 

 poral muscle ; and the lower boundary of this depression is formed by a strong 

 ridge extended downward and forward from the outside of the condyle. But in the 

 Dog and other placental Carnivores (the Seals excepted), a process, representing 



* Ossem. Fossiles, Ed. 8% 1835, vol. v. p. 524. 



