

 428 A MANUAL OF DENTAL ANATOMY. 



already been drawn on account of its size and other pecu- 

 liarities, by virtue of its great size displaces not only the 

 milk molar, to which it is the legitimate successor, but also 

 turns out the second premolar, a tooth belonging to the 

 " permanent " series. 



In this particular the succession of the teeth in the 

 Hypsiprymnus is the same as that of the true kangaroos, 

 which may be understood by a reference to fig. 190. 



There are two extinct Marsupials, known only by their 

 jaws, which have been the subject of much controversy. 

 Professor Owen, basing his arguments largely upon the 

 presence of premolars which possessed elongated and sharp- 

 edged blades, held that Plagiaulax and Thylacoleo were 

 carnivorous, saying of the latter that it possessed the simplest 

 and most effective dental machinery for predatory life known 

 among Mammalia ; Dr. Falconer, in the case of the first, and 

 Professor Flower in the case of the Thylacoleo, having shown 

 this view to be untenable, or at least unsupported by adequate 

 evidence. 



The clue to the nature of the great blade-shaped teeth of 

 these two extinct creatures is afforded by the form of the 

 premolar of the herbivorous Hypsiprymnus (see fig. 189). 

 The incisors were reduced in number and were large ; the 

 teeth between them and the large premolar were stunted ; 

 but both these points are true of the herbivorous kangaroos. 

 The Thylacoleo differs, however, from all known animals by 

 the immense size of the thin-edged premolar (worn flat in 

 aged animals), and by the rudimentary condition of its true 

 molars. But its incisors, lying forwards and closely ap- 

 proximated in the middle line, are particularly unsuitable 

 for catching and holding anything alive and struggling, 

 whilst the nearest resemblance to the blade-shaped tooth is 

 to be found in harmless herbivorous creatures, so that the 

 balance of evidence is much against Professor Owen's view. 

 It has been cited here merely as an instance of how the 

 evidence afforded by teeth alone may be misleading. 



