SUCCESSION OF THE TEETH IN THE MARSUPIALIA. 
637 
In the lower jaw the first and third incisors lie superficially, the second being deeply 
placed between them, — a relation which may also be observed in the fangs of these teeth 
in the adult animal. The canine is deeply placed in the bone, its crown partially 
concealed from the outer side by the third incisor and first premolar. The third pre- 
molar is placed lowest in the mandible, its apex is nearly in contact with the inner 
side of the base of the rudimentary temporary molar. The crown of the first molar is 
completely calcified, that of the second and third partially so ; no germ of the fourth 
could be traced. 
The dentition above described is one of the most interesting and instructive in the 
whole series. It would be desirable to examine the teeth of some member of the allied 
genus Dasyurus at a corresponding age, but of this I have as yet had no opportunity. 
Family Phascolomyida:. 
I have placed this family at the end of the series, only because it is the one upon the 
dentition of which there is the least satisfactory information. 
In a young Wombat ( Phascolomys vombatus ) 11 inches in length, the tips of the 
incisors, and of the premolars and first two molar teeth, were just appearing through 
the gums. The extent to which calcification had taken place in these teeth and the 
third molar is shown in Plate XXX. fig. 7. A trace of the germ of the fourth molar 
was discernible. There were no vestiges of successional teeth. 
It is stated of this genus by Professor Owen that “ the incisors and the first molar 
tooth are shed when the animal is young ; the latter is superseded by the premolar 
tooth” *. Without further evidence, the statement as to the first may well be questioned, 
for even in the Rodents it has never been shown that the scalpriform incisors have deci- 
duous predecessors ; while, on the other hand, the analogy with the remaining marsupial 
families fully bears out the second. No details as to the mode or period at which this 
change occurs are given. It remains, therefore, for those who have opportunities of 
examining young Wombats at various ages to ascertain whether the first tooth of the 
molar series shown in the figure has already replaced, or is about to be replaced by 
another. Judging from its characters, which resemble those of the so-called “ premolar’’ 
of the adult and not one of the true molars, I have very little hesitation in pointing to 
the former conjecture as the one most likely to prove correct. 
From the foregoing observations, embracing members of each of the six natural 
families of the Marsupialia, it may be safely concluded that the animals of this order 
present a peculiar condition of dental succession, uniform throughout the order, and 
distinct from that of all other mammals. 
This peculiarity may be thus briefly expressed. The teeth of Marsupials do not 
vertically displace and succeed other teeth, with the exception of a single tooth on each 
side of each jaw. The tooth in which a vertical succession takes place is always the 
* Odontography (1840-45), p. 394. 
