OF THE MARSUPIALIA. Bee 
Tribe V. RHIZOPHAGA. 
The characters of this tribe are taken from the stomach, which is simple in outward 
form, but complicated within by a large cardiac gland ; and from the cecum, which is 
short and wide, with a vermiform appendage. 
Genus Phascolomys. 
In its heavy shapeless proportions, large trunk, and short equably developed legs, the 
Wombat offers as great a contrast to the Kangaroos as does the Koala, which it most 
nearly resembles in its general outward form and want of tail. But in the more im- 
portant characters afforded by the teeth and intestinal canal the Wombat differs more 
from the Koala than this does from either the Phalangers or Kangaroos. The dental 
system presents the extreme degree of that degradation of the teeth intermediate be- 
tween the front incisors and true molars which we have been tracing from the Opos- 
sum to the Kangaroos: not only have the functionless spurious molars and canines 
now totally disappeared, but also the posterior incisors of the upper jaw, which we have 
seen in the Potoroos to exhibit a feeble degree of development as compared with the 
anterior pair ; these in fact are alone retained in the dentition of the present group, which 
possesses the fewest teeth of any Marsupial animal. The dental formula of the Wombat 
is thus reduced to that of the true Rodentia’: 
Incisors . canines a3 premolars 3 molars ee = 24. 
The incisors, moreover, are true dentes scalprarii, with persistent pulps, but are in- 
ferior, especially in the lower jaw, in their relative length, and curvature, to those of the 
placental Glires: they present a subtrihedral figure, and are traversed by a shallow 
groove on their inner surfaces. 
The spurious molars present no trace of that compressed structure which character- 
izes them in the Koala and Kangaroos : but have a wide, oval, transverse section ; those 
of the upper jaw being traversed on the inner side with a slight longitudinal groove. 
The true molars are double the size of the spurious ones: the superior ones are also 
traversed by an internal longitudinal groove, but this is so deep and wide, that it divides 
the whole tooth into two trihedral portions, with one of the angles of each prism di- 
rected inwards. The inferior molars are in like manner divided into two trihedral 
portions, but the intervening groove is here external, and one of the faces of each prism 
is turned inwards. All the grinders are curved, and describe about a quarter of a 
circle ; in the upper jaw the concavity of the curve is directed outwards, in the lower 
* All the placental Rodents which have more than three molars in each lateral series have the additional ones 
situated at the anterior part of the series, and subject to vertical displacement and succession, and consequently 
these are essentially premolars: the Wombat strikingly manifests its marsupial character in having four true 
molars on each side of both jaws. 
VOL. II.—PART IY. ras 
