54 Mr. Owen on the Thylacotherium. 



The double fangs of the seven anterior molars in place are exposed by the break- 

 ing away of the internal plate of the ramus of the jaw : in the three following 

 molars the beginning of the fangs are visible, slightly protruded from their sockets. 

 The fangs extend half way through the vertical diameter of the ramus ; their dense 

 ivory is clearly contrasted both by its texture and deeper colour from the sur- 

 rounding bone : so far from being anchylosed to this bone, as M. De Blainville 

 asserts, they are clearly separated from it by a thin layer of a distinct colour from 

 either, and which appears to be due to the matrix which has insinuated itself into 

 the sockets of the teeth, as it has into the vascular canals of the jaw. 



Lastly, it must be obvious to all who inspect this fossil and compare it with the 

 jaw of a small Didelphys, that, contrary to the assertion of M. de Blainville, the 

 teeth and their fangs are arranged with as much regularity in the one as in the 

 other ; and that instead of an argument in favour of the saurian nature of the 

 fossil being afforded by this part of its structure, the distinct sockets and their 

 double cavities, corresponding with the long and slender double fangs of the teeth, 

 are conclusive against the saurian theory. 



I proceed next to the description of the second specimen of the half -jaw of 

 Thylacotherium Prevostii in Dr. Buckland's collection (PI. V. fig. 1) : this agrees 

 in size and form with the preceding. Such teeth as are preserved in it, agree with 

 the corresponding ones in the previous specimen : there can be no doubt that they 

 both belonged to mature individuals of the same species and the same size. M. Va- 

 lenciennes, after an inspection of this second example, declared it to be the left 

 ramus of the lower jaw, having its internal side exposed to view : he founded his 

 opinion on the presence of the orifice of the dental canal near one end, and of 

 the articular surface of the symphysis at the other. 



M. de Blainville, after an inspection of the casts of this example, came to a con- 

 trary opinion ; he denies the existence of the orifice of the dental canal and of the 

 symphysial articulation, and describes the specimen in question as being the ex- 

 ternal side of a compound jaw with an articular notch, like that of a fish or reptile. 

 It has become necessary, therefore, again to subject this specimen to a severe 

 scrutiny ; and M. Valenciennes will pardon me for reiterating facts which he has 

 so ably and accurately described, when he reflects that the progress of geological 

 truth and the establishment of a sound theory of the succession of animal develop- 

 ment in this planet would be impeded, if the doubts, cast upon his statements by 

 so able an anatomist as his learned colleague, should remain untested by a second 

 appeal to the specimen itself. 



In this specimen the whole of the exposed surface of the lower jaw, with the ex- 

 ception of the coronoid, articular and angular processes, is entire ; the smooth 

 surface near the anterior extremity of the jaw is in bold relief, and slopes away at 



