Geological Society. 205 



" Thylacotherium," described in the first part of the memoir*, and 

 which he conceives fully prove the mammiferous nature of that 

 fossil. He stated, that the remains of the split condyles in the spe- 

 cimen demonstrate their original convex form, which is diametrically 

 opposite to that which characterizes the same part in all reptiles 

 and all ovipara ; — that the size, figure and position of the coronoid 

 process are such as were never yet witnessed in any except a 

 zoophagous mammal endowed with a temporal muscle sufficiently 

 developed to demand so extensive an attachment for working 

 a powerful carnivorous jaw; — that the teeth, composed of dense 

 ivory with crowns covered with a thick coat of enamel, are everywhere 

 distinct from the substance of the jaw, but have two fangs deeply im- 

 bedded in it ; — that these teeth, which belong to the molar series, 

 are of two kinds ; the hinder being bristled with five cusps, four of 

 which are placed in pairs transversely across the crown of the teeth, 

 and the anterior or false molars, having a different form, and only 

 two or three cusps — characters never yet found united in the teeth 

 of any other than a zoophagous mammiferous quadruped ; — that the 

 general form of the jaw corresponds with the preceding more essen- 

 tial indications of its mammiferous nature. Fully impressed with 

 the value of these characters, as determining the class to which the 

 fossils belonged, Mr. Owen stated, that he had sought in the next 

 place for secondary characters which might reveal the group of 

 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 Thylacotherium 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 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- 



* An abstract of the first part of Prof. Owen's memoir was given at p. Gl 

 of the present volume. — Edit, 



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