Prof. Owen on the Phascolotherium. 221 



mammalia to which the remains could be assigned, and that he 

 had found in the modification of the angle of the jaw, combined 

 with the form, structure and proportions of the teeth, sufficient 

 evidence to induce him to believe, that the Tliylacotherium was a 

 marsupial quadruped. 



Mr. Owen then recapitulated the objections against the mammi- 

 ferous nature of the Thylacotherian jaws from their supposed imperfect 

 state ; and repeated his former assertion, that they are in a condition 

 to enable these characters to be fully ascertained : he next reviewed 

 first the differences of opinion with respect to the actual structure 

 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 condjde, 

 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 Insectivora 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 zooi^ha- 

 gous Cetacea offer still more numerous and reptile-Hke 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 /<?;■« 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 tliat 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 cxi)lained, that the widely bifurcate basis support- 

 ing the tooth of tlie shark, is no part of tlie actual tootli, but true 

 bone, and ossified parts of the jaw itself, to which the tooth is an- 



