392 PROF. OWEN ON THE OSTEOLOGY 
osteological science has been called in question by other naturalists, and has been 
more especially opposed by Prof. Blainville, who conceives it to be more probable that 
they belong to a genus of Saurian Reptiles than to the Didelphys, or any genus of insec- 
tivorous Mammals. I have examined the two specimens in the possession of Dr. Buck- 
land, the specimen formerly in the collection of Mr. Broderip, and that which is pre- 
served in the Museum at York. The simple structure of the lower jaw, each ramus of 
which consists of one piece of bone, the convex condyle, and the double fangs of the 
molar teeth, prove the mammiferous character of these remains ; the size, elevation and 
form of the coronoid process of the lower jaw, the production of the angle of the jaw, 
with the development of the canines, and the pointed tubercular crowns of the molar 
teeth, indicate the carnivorous and insectivorous character of the species in question. 
The number of the incisors, eight in the lower jaw, and the structure and proportions 
of the molar teeth, approximate these small Insectivora most nearly to the smaller spe- 
cies of the modern genus Didelphys ; but the number of the molars in one of the speci- 
mens exceeds that of any Insectivore, placental or marsupial, which was known at the 
period when Cuvier wrote on this fossil. Recently, however, a genus of insectivorous 
Mammal (Myrmecobius) has been discovered in Australia, presenting the modifications 
of the cranium which characterize the Marsupiata, and having nine tuberculate molars 
in each ramus of the lower jaw’. Besides the osteological characters above alluded to, 
there is a character in the lower jaw of the marsupial animals, not peculiar to the genus 
Didelphys, which serves to distinguish it from that of the placental Mammalia. In the 
carnivorous Marsupials, as the Thylacine, the lower maxillary bone very nearly resem- 
bles in general form that of the corresponding placental species, as the Dog : a similar 
transverse condyle is placed low down near the angle of the jaw; the strong coronoid 
process rises high above it, and is slightly curved backwards ; there is the same well- 
marked depression on the exterior of the ascending ramus for the firm implantation of. 
the temporal muscle, and the lower boundary of this depression is formed by a strong 
ridge extended downwards and forwards from the outside of the condyle. But in the 
Dog, and other placental digitigrade Carnivora, a process, representing the angle of the 
jaw, extends directly backwards from the middle of the above ridge, which process gives 
fixation to the articulation of the jaw, and increases the power by which the masseter 
acts upon the jaw. Now although the same curved ridge of bone bounds the lower 
part of the external depression of the ascending ramus in all the Marsupiata, it does not 
in any of them send backwards, or in any other direction, a process corresponding to 
that just described in the Dog. The angle of the jaw is as if it were bent inwards in 
the form of a process, encroaching in various shapes and various degrees of develop- 
ment in the different marsupial genera upon the interspace of the rami of the lower jaw. 
In looking down upon the lower margin of the jaw, we see, therefore, in place of the 
1 See Mr. Waterhouse’s Memoir, Zool. Trans. Vol. ii, Pl. XXVIII. figg. 2, 5. 
