504 CHORDATA. 
jumping. At rest the kangaroo places the whole foot on the ground. 
All are strictly herbivorous and the stomach is complex, the front part 
being sacculated and containing the cesophageal and cardiac glands. The 
true kangaroos and wallabies are cursorial, playing the part of antelopes 
or deer in the districts they frequent. The rat-kangaroos are smaller, 
ae and partially fossorial. Others, the tree-kangaroos, are 
arboreal, 
Family II.—Phalangeridz.—A family containing a great number 
of small arboreal animals. They are usually woolly and often have a 
prehensile tail. In addition, a number of them have a flap of skin or 
patagium which enables them to ‘“‘sail” from tree to tree (incidental 
zrial). From these habits it is not surprising to find five toes all 
present on each limb and the hallux opposable to the other four. 
These phalangers approach more nearly the Polyprotodontza, especially 
as they have additional small functionless incisors in the lower jaw, and 
their diet is by no means strictly herbivorous. The common koala 
(Phascolarctos) and the flying squirrels (Petaztrzs) should be noted. 
Family IIJ.—Phascolomyidz.—A very small family, consisting 
of about three species of wombats. The wombat (Phascolomys) is a 
small bear-like terrestrial or partially fossorial animal. All five digits 
are retained on both limbs and the syndactylism is not very pronounced. 
But the peculiar dentition is the great feature of this form. Just as 
similar external conditions cause a resemblance of the Tasmanian wolf 
( Thylacinus) to the dog, or Notoryctes to a mole, so here we have a 
metatherian repetition of the eutherian rodent. There is one pair of 
incisors in each jaw; they grow 
Fig. 349.—PosTERIOR VIEW OF from persistent pulps and have 
Lower Jaw oF Womsat. enamel only on the front surface. 
There are no canines and there 
is a large space or diastema 
between the incisors and the 
‘* cheek-teeth.”” These are five 
in number, one premolar and 
four molars; a is the formula. 
Family IV.—Epanorthide. 
—Another small family which 
contains a remarkable little ani- 
mal, the selva or opossum-rat 
Showing inflected angle. (Cenolestes). The selvas have 
recently been found alive in S. 
America though they were supposed to be extinct. They are dipro- 
todont in their lower jaw, but the teeth of the upper jaw more nearly 
resemble certain of the Polyprotodontia. They differ from the rest of the 
Diprotodontia in not having a syndactylous foot, though doubtful traces 
of syndactylism in some of their fossil allies have been stated to exist. 
DisTRIBUTION OF DIPROTODONTIA.—The families of the 
kangaroos, phalangers and wombats, in fact nearly all the 
