80 PROFESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 



chief molar teeth. In Felis the small incisors are very little in advance of the canine ; 

 this large tooth is almost at the fore part of both upper and lower jaws; and in Thyla- 

 coleo the relative position of the incisor-tusk to the enormous temporal fossa is such as 

 to give it the advantage of a harder or closer grip during the action of the powerful 

 temporal muscles. 



In the former paper so much of the characters of the lower jaw, and its teeth, of Thy- 

 lacoleo were given as could be deduced from the cast of a portion of that bone figured 

 in Plates XI. & XIII. figs. 3, 4, & 5, pp. 317 & 318, of the Philosophical Transactions 

 for 1859. 



The camassial and succeeding tubercular teeth, being in place, served to refer this 

 fossil to the same species as that indicated by the upper jaw (Plate XI. figs. 1 &2, tom.cit.)^ 

 A socket for a second smaller " tubercular " was evident, behind the one in place. The 

 chief doubt remained in regard to the fore part of the mandibular ramus ; the plaster- 

 cast did not admit of any certain conclusion as to the extent to which the original 

 might there have sufiered fracture ; part of the symphysial surface and the base or 

 socket of a large obliquely produced tooth could be made out, and this " seemed to be 

 the sole tooth in advance of" the carnassial. Accordingly I wrote, "If the ramus be 

 really produced at the upper part of the symphysis further than is indicated in the 

 present cast, it may have contained one or more incisors, and the broken tooth in 

 question may be the lower canine. If, however, this be really the foremost tooth of the 

 jaw, it would appear to be one of a pair of large incisors, according to the marsupial 

 type exhibited by the MacropodidcB and Phalangistidce " {loc. cit. p. 318). 



The perfect condition of the upper jaw of the chief subject of the present paper 

 determined the alternative, and proved the Thylacoleo to be the carnivorous modifica- 

 tion of the more common and characteristic type of Australian Marsupials, having the 

 incisors of the lower jaw reduced to a pair of large, more or less procumbent and 

 approximate, conical teeth or " tusks." 



I have been favoured by Mr. Geraed Krefft, the able Curator of the Australian 

 Museum, Sydney, New South Wales, with a " photograph " of the outer side, and an 

 outline sketch, natural size, of the inner side, of a portion of the right mandibular 

 ramus of Thylacoleo carnifex in that Museum, which presents the same general resem- 

 blance, in the kind and degree of mutilation, to the original of the cast described in 

 Part I., which the cranium from the " Condamine River " presents to the one from 

 " Colungoolac." It is fortunately, however, a little more complete ; sufficiently so to 

 demonstrate that the large socket (Plate IV. figs. 5 & 6, i) is of the foremost tooth 

 of the lower jaw. It also exhibits two small approximate alveoli, or the divisions of 

 an alveolus, for a two-fanged tooth, corresponding in size and in relative position to the 

 carnassial, with the similar socket or sockets noticed in the description of the upper 

 jaw (Plate III. p s). There are evidently no smaller incisors behind the large one of 

 the lower jaw, nor any other teeth between the large incisive tusk and the small tooth 

 or teeth on the inner side of the fore part of the great lower carnassial. The portion of 



