18 
of the jaw; and, secondly, to the interpretation of admitted appear- 
ances. 
1. As respects the structure.—It has been asserted that the jaws 
must belong to cold-blooded vertebrata, because the articular sur- 
face is in the form of an entering angle; to which Mr. Owen 
replies, that the articular surface is supported on a convex condyle, 
which is met with in no other class of vertebrata except in the 
mammalia. Again, it is asserted, that the teeth are all of an uni- 
form structure, as in certain reptiles; but, on reference to the fos- 
sils, Mr. Owen states, it will be found that such is not the case, and 
that the actual difference in the structure of the teeth strongly sup- 
ports the mammiferous theory of the fossils. 
2. With respect to the argument founded on an interpretation of 
structure, which really exists, the author showed, that the Thylaco- 
therium, having eleven molars on each side of the lower jaw is no 
objection to its mammiferous nature, because among the placental 
carnivora, the Canis Megalotis has constantly one more grinder on 
each side of the lower jaw than the usual number; because the 
Chrysochlore among the Jnsectivora has also eight instead of seven 
molars in each ramus of the lower jaw; and the Myrmecobius, 
among the Marsupialia, has nine molars on each side of the lower 
jaw ; and because some of the insectivorous Armadillos and zoophas 
gous Cetacea offer still more numerous and reptile-like teeth, with all 
the true and essential characters of the mammiferous class. The ob- 
jection to the false molars having two fangs, Mr. Owen showed 
was futile, as the greater number of the spurious molars in every 
genus of the placental fere have two fangs, and the whole of them 
in the Marsupialia. If the ascending ramus in the Stonesfield jaws 
had been absent, and with it the evidence of their mammiferous 
nature afforded by the condyloid, coronoid and angular processes, 
Mr. Owen stated, that he conceived the teeth alone would have 
given sufficient proof, especially in their double fangs, that the 
fossils do belong to the highest class of animals. 
In reply to the objections founded on the double fangs of the 
Basilosaurus, Mr. Owen said, that the characters of that fossil, not 
having been fully given, it is doubtful to what class the animal be- 
longed; and, in answer to the opinion, that certain sharks have 
double fangs, he explained, that the widely bifurcate basis support- 
ing the tooth of the shark, is no part of the actual tooth, but true 
bone, and ossified parts of the jaw itself, to which the tooth is an- 
chylosed at one part, and the ligaments of connexion attached at the 
other. The form, depth and position of the sockets of the teeth in 
the Thylacothere are precisely similar to those in the small opos- 
sums. The colour of the fossils, Mr. Owen said, could be no ob- 
jection to those acquainted with the diversity in this respect, which 
obtains in the fossil remains of Mammalia. Lastly, with respect to 
the Thylacothere, the author stated, that the only trace of compound 
structure is a mere vascular groove running along its lower margin, 
and that a similar structure is present in the corresponding part of 
the lower jaw of some species of opossum, of the Wombat, of the 
