Mr. Owen on the Thylacotherium. 49. 



Comparative Anatomy at the Jardin des Plantes has declared, after an inspection 

 of casts of the fossil examined by Cuvier and Valenciennes, that these anatomists 

 have been deceived in all those points. M. de Blainville {loc. cit.) asserts that 

 there is no trace of a convex condyle, but that, in its place, there exists an arti- 

 cular fissure, somewhat as in the jaws of Fishes ; that the teeth, instead of being 

 imbedded in sockets, have their fangs confluent with, or anchylosed to, the sub- 

 stance of the jaws ; and that the jaw itself presents evident traces of the composite 

 structure. 



The point, therefore, which first demands our closest attention, is the actual 

 condition in the Stonesfield fossils of the articular or condyloid process. Now it 

 is scarcely necessary to observe, that the condyle of a lower jaw, independently 

 of any other part, is sufficient to indicate whether it belongs to a mammiferous or 

 oviparous animal. In the Mammalia it is convex or flat, in all Ovipara it is con- 

 cave ; in the fossil Stonesfield jaw examined by Cuvier (PI. V. fig. 3), in the 

 second specimen of the same species (PI. V. fig. 1) examined by M. Valenciennes, 

 and in the lower jaw of another genus (PI. VI. fig. 2), described and figured by 

 Mr. Broderip*, a prominent, convex, articular condyle is more or less distinctly 

 revealed. It is most entire and unequivocal in Mr. Broderip's specimen, which 

 I shall subsequently describe. What M. de Blainville has mistaken for an ar- 

 ticular fissure — " une sorte d'echancrure articulaire un pen comme dans les 

 poissons," — must be the entering angle or notch either above or below the true 

 articular condyle. 



In Plate II. fig. 1 of the Bridgewater Treatise of Dr. Buckland, this important 

 part of the structure of the jaw is very accurately represented. The figure also of 

 the jaw of the Thylacotherium, given by M. Prevost in the Annales des Sciencesf, 

 is by no means " tout-k-fait inexacte," as asserted by M. de Blainville ; but the 

 form of the condyle is less completely displayed in this fossil than in the second 

 specimen of Thylacotherium Prevostii, Val. (PI. V. fig. 1). Although mutilated 

 in both, what remains is situated in a line parallel with the crowns of the teeth, 

 and projects beyond the vertical line dropped from the extremity of the coronoid 

 process. 



In the example examined by Cuvier, the form and extent of the coronoid pro- 

 cess is indicated in a very clear and well-defined manner by the impression which 

 it has left upon the matrix. 



Now the coronoid process of the Opossum's jaw is plane on its inner surface, 

 but slightly convex on the outer surface, the anterior margin of the process being 

 produced externally in the form of a smooth convex ridge ; and both this ridge 

 and the shallow depression behind it, are accurately represented in the impression 

 which this portion of the jaw has left on the matrix in which it was imbedded. 



* Zoological Journal, vol. iii. p. 408, PI. XL. f Avril 1825, PI. XVIII. fig. 1, p. 389. 



VOL. VI. SECOND SERIES, H 



