Geohf/kal Society. 209 



artery, and that the author possesses the jaw of a Didelphys Virgi- 

 niana which exhibits a similar ^a'oove in the same place. Moreover, 

 this groove in the Phascolothere does not occupy the same relative 

 position as any of the contiguous margins of the opercular and den- 

 tary pieces of a reptile's jaw. The other impression in the jaw of 

 the Phascolotherium is a deep groove continued from the anterior 

 extremity of the fractured base of the inflected angle obliquely 

 downwards to the broken surface of the anterior part of the jaw. 

 Whether this line be due to a vascular impression, or an accidental 

 fracture, is doubtful ; but as the lower jaw of the Wombat presents an 

 impression in the precisely corresponding situation, and which is 

 undoubtedly due to the presence of an artery, Mr. Owen conceives 

 that this impression is also natural in the Phascolothere, but equally 

 unconnected with a compound structure of the jaw ; for there is 

 not any suture in the compound jew of a reptile which occupies a 

 corresponding situation. 



The most numerous, the most characteristic, and the best marked 

 sutures in the compound jaws of a reptile, are those which define the 

 limits of the coronoid, articular, angular, and surangular pieces, and 

 which are chiefly conspicuous on the inner side of the posterior part of 

 the jaw. Now the corresponding surface of the jaw oi the Phascolo- 

 there is entire ; yet the smallest trace of sutures, or of any indication 

 that the coronoid or articular processes were distinct pieces, cannot be 

 detected ; these processes are clearly and indisputably continuous, 

 and confluent with the rest of the ramus of the jaw. So that 

 where sutures ought to be visible, if the jaw of the Phascolothere 

 were composite, there are none ; and the hypothetical sutures that 

 are apparent do not agree in position with any of the real sutures 

 of an oviparous compound jaw. 



Lastly, with reference to the philosophy of pronouncing judg- 

 ment on the saurian nature of the Stonesfield fossils from the 

 appearance of sutures, Mr. Owen ofl'ered one remark, the justness 

 of which, he said would be obvious alike to those who were, and 

 to those vAio were not, conversant with comparative anatomy. The 

 accumulative evidence of the true nature of the Stonesfield fossils, 

 afforded by the shape of the condyle, coronoid process, angle of the 

 jaw, different kinds of teeth, shape of their crowns, double fangs, 

 implantation in sockets, — the appearance, he repeated, presented 

 by these important particulars cannot be due to accident ; while 

 those which favour the evidence of the compound structure of the 

 jaw may arise from accidental circumstances. 



Ann. Nat. Hist, Vol.3. IS o. 16. May ISS9. q 



