Mr. Owen on the Thylacotherium. 53 



are vertically split, and more or less of their internal grinding surface is broken 

 away. 



The tenth molar presents only the inner side of the middle external cusp, with 

 part of the anterior cusp ; a similar appearance would be produced in the true 

 molar of a Didelphys, if the internal middle cusp and the posterior cusps were ob- 

 liquely sliced away. 



In the ninth molar the large middle external cusp is nearly entire to its sharp 

 apex ; part of the anterior cusp and the base of the internal posterior cusp are pre- 

 served : the same appearances would be produced in the true molar of a Didelphys, 

 if the middle internal cusp and part of the anterior and posterior internal cusps 

 had been obliquely truncated. 



In the eighth tooth the fractured surface of the crown gives a view of the anterior 

 and large middle external cusp, with part of the posterior external cusp. 



In the seventh tooth the crown is more mutilated than in the preceding teeth ; only 

 a part of the anterior cusp and the base of the external cusp are visible ; but the 

 fracture displays the breadth of the crown, and corroborates the evidence afforded 

 by the preceding teeth, and confirmed beyond question by the posterior molar of 

 the second jaw (PI. V. fig. 1), that these posterior molars were not provided, as 

 M. de Blainville asserts, with mere compressed, five-lobed crowns. 



In the sixth tooth the evidence of the complicated structure of the crown 

 becomes indistinct : part of a large anterior and small posterior cusp are alone 

 visible.' 



In the fifth tooth two similar cusps are present, but the points are broken. 



The crowns of the fourth, third and second grinders are perfect, and clearly show 

 that they are each divided into two, and not three, sub-compressed conical cusps, the 

 posterior one being very much less than the other : these teeth precisely resemble 

 the second and third false molars of the lower jaw in the Mole, as well as in some 

 species of Didelphys. I cannot perceive the tricuspid structure given to these 

 teeth in the figure in the Bridgewater Treatise of the jaw now described ; that of 

 M. Prevost in the Annales des Sciences is more exact in this particular, at least 

 as regards the third tooth in place. 



The minute cylindrical medullary canal {cavitas pulpi) is plainly visible in the 

 anterior fang of both the second, third, fourth and fifth molars. 



The crowns of the first and second premolars in the present specimen are broken 

 vertically like the posterior teeth ; but sufficient of the crown is preserved in both 

 to show that it was unequally bicuspid, as in the two succeeding false molars. 



The anterior false molars are altogether displaced ; but traces of the alveoli, for 

 the two short fangs of one of these, may be perceived at the broken anterior ex- 

 tremity of the present fossil. 



