TEETH OF DIPHYODONTS. 291 



subquadrate crowns ; each presents four three-sided pyramidal 

 cusps ; but the internal angles of the two opposite cusps are con- 

 tinued into each other across the tooth, forming two angular or 

 concave tranverse ridges. In the old animal these cusps and 

 ridges disappear, and the grinding surface is worn quite flat. 



In the genus Macropus, fig. 231, the normal condition of the 

 permanent teeth may be expressed as follows : — 



.3.3 0.0 1.1 4.4 OQ 



l n ;c o^ ; ^Li ;m 4^ = 28 - 



The main difference, as compared with Hypsiprymnus, lies in the 

 absence of the upper canines as functional teeth ; but the germs 

 of these teeth are to be found in the young mammary foetus of 

 the Macropus major, and may be detected of very small size, 

 concealed by the gum, in the adults of some small species of 

 Kangaroos, as, e. g., Macropus rufiventer, Ogilby, and Macr. 



Dentition of Macropus major, one-third nat. size. 



psilopus, Gould. The crown of the true molars supports two 

 principal transverse ridges, with a broad anterior talon and a narrow 

 hinder one. In most species a spur is continued from the hinder to 

 the fore ridge, and another from the fore ridge to the front talon. 



Remains of Kangaroos, larger than any living species, have been 

 discovered in the same caves in Australia which contained the teeth 

 and jaws of the extinct Dasyurus laniarius, and they probably formed 

 the prey of that species and of its contemporary the Thylacine 

 which no longer exists in the continent of Australia. 1 



A gigantic extinct herbivorous Australian Marsupial (Dipro- 

 todon), the bulk of which may be surmised from the length 

 of the skull, which equals three feet, manifests a dentition 

 which makes the nearest approach to that of the Kangaroos ; 

 but the anterior or median pair of upper incisors present the 

 condition of large, curved, scalpriform, ever-growing tusks, 



1 cxvin", vol. ii. 

 u 2 



