108 
LOWER MAM:\fAL GALLERY. 
This structure of the foot is not confined to tlie Kangaroos, but 
is also found in certain of the other families. 
Kangaroos vary in size from species belonging to the typical 
genus Macropus (1396 to 1406) as large as a man, through the 
smaller kinds known as Wallabies (fig. 58), to others smaller 
than a Eabbit, such as the Kangaroo-Rats, or Rat-Kangaroos, 
Potorous (1415, 1416). Of those exhibited may be specially 
mentioned the Great Red Kawg'avoo, Macrojms rufus (1405), the 
largest of the family, and the beautiful Yellow-footed Wallaby, 
Petrogale xantliopus (1410), the most brightly-coloured species 
of the group, as well as a species of Tree-Kangaroo, Penclro- 
/up'?f5(1411 & 1412). Very curious, too, is the little Musk- 
Kangaroo, Ilypsiprymnodon moscliatus (1422). 
In Kangaroos and Wallabies the dental formula, when fully 
developed, is I. f, C. P. -}-M. §=34 ; some of the front 
grinding-teeth, however, are generally lost before the hinder 
ones are in position. 
Numerous fossil remains of animals allied to Kangaroos, 
some as large as a Rhinoceros, have been found in the super- 
ficial deposits of Australia, among which may be specially 
mentioned the huge Diprotodon australis (1425), of which a 
cast of the lower jaw is exhibited in case 69. A fine series of 
remains is shown in the Palseontological Gallery. 
[Case 70.] The Australian Opossums and their relatives, collectively 
known as Phalangers {Phalangeridcc) , differ from the Kangaroo 
group by the possession of a large opposable great toe and the 
comparative shortness of their hind-feet. The teeth are variable 
in form and number, the genera of the family being founded 
almost entirely on these variations. The dental formula ranges 
from I. f, C. I, P.-bM. 1 = 28, to I. f, C. j, P + M. f = 40. 
In the curious larsipes rostratus (1446) the molar teeth are so 
reduced and variable that no definite number can be assigned to 
it. The hind-feet are of the same type as in the Kangaroos, 
but the disproportion between the bones of the united second 
and third toes on the one hand, and the fourth on the other, is 
not so great as in those animals. 
The members of this group vary in size from that of a Mouse, 
