MARSUPIALIA. 



267 



true molar has cut the gum : the succeeding 

 true molar is soon afterwards extruded ; and 

 I have seen a skull of an old Macropits major 

 in the Museum at Leyden, in which the 

 grinders were reduced to two on each side of 

 each jaw by this yielding of the anterior ones 

 to the vis a tergo of their successors. 



The general form of the body in the Mu- 

 cropvdidtf is that of an elongated cone, the 

 broad and stout haunches forming the base, 

 and the produced tapering muzzle the apex. 

 The proportions of the body are, however, re- 

 duced by so elegant a gradation that they are 

 justly considered as among the most picturesque 

 of quadrupeds. The hinder extremities are al- 

 ways longer and stronger than the fore ones, but 

 in various proportions ; the difference being least 

 in the arboreal Potoroos, and in that section of 

 the genus represented by the Hypsiprymnus 

 myosurus of Van Dieman's Land. The tail is 

 very long in all the species, but is strongest in 

 the great kangaroos, which make use of it as a 

 kind of crutch or fifth extremity in their slower 

 modes of progression. In the Potovoos the 

 tail is more slender, and in these and some of 

 the smaller species of kangaroo it is bent be- 

 neath the body when the animal reposes. 



Tribe V . R HIZO PHAGA. 



In this tribe, the stomach is simple in out- 

 ward form, but complicated within by a large 

 cardiac gland ; and the co3cum, which is short 

 and wide, with a vermiform appendage. 

 Genus PHASCOLOMYS, (Jig. 93.) 



In its heavy shapeless figure, large trunk, 

 and short equably developed legs, the Wom- 

 bat offers as great a contrast to the Kangaroos as 



Fig. 93. 



Phascolomysfusca, Geoff, one-half nat. size. 



does the Koala, which it most nearly resembles 

 in its general outward form and want of tail. 

 But in the more important characters afforded 

 by the teeth and intestinal canal, the Wombat 



succeeded in the vertical direction by a permanent 

 spurious molar, as in the Halmaturi, it was dis- 

 placed by the true molars, which are developed 

 from behind forwards. 1 have however detected the 

 crown of the permanent spurious molar in the jaws 

 of the Macropus major in a concealed alveolus, and 

 have observed it completely formed and in place 

 in an individual which had nearly attained its full 

 size. See F. Cuvier's account of the Halmaturus 

 Thetis in the " Histoire dcs Mammiferes," folio. 



differs more from the Koala than the latter does 

 from either the Phalangers or Kangaroos. 



The dental system presents the extreme de- 

 gree of that degradation of the teeth, interme- 

 diate between the front incisors and true molars, 

 which we have been tracing from the Opossum 

 to the Kangaroos : not only have the function- 

 less premolars and canines now totally disap- 

 peared, 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, the representative of which possesses 

 the fewest teeth of any Marsupial animal. The 

 dental formula of the Wombat is thus reduced 

 both in number and kind to that of the true 

 Rodentia.* 



Incisors. _ : canines, - ; premolars, . _ 

 2 1 1' 



4 4 



molars, = 24. 



4 4 



The incisors moreover are true denies scalpru- 

 rii, with persistent pulps, but are inferior, espe- 

 cially in the lower jaw, in their relative length 

 and curvature to those of the placental Glires; 

 they presentasubtriedral figure, and are traversed 

 by a shallow groove on their mesial surfaces. 



The spurious molars present no trace of that 

 compressed structure which characterizes them 

 in the Koala and Kangaroos, but have a wide 

 oval transverse section ; those of the upper jaw 

 being transversed on the inner side with a 

 slight longitudinal groove. The true molars 

 are double the size of the premolars : the su- 

 perior ones are also traversed by an internal 

 longitudinal groove, but this is so deep and 

 wide that it divides the whole tooth into two 

 prismatic portions, with one of the angles 

 directed inwards. The inferior molars are 

 in like manner divided into two triedral 

 portions, but the intervening groove is here 

 external, and one of the facets of each 

 prism is turned inwards. All the grinders 

 are curved, and describe about a quarter 

 of a circle : in the upper jaw the con- 

 cavity of the curve is directed outwards ; 

 in the lower jaw, inwards. The false and 

 true molars, like the incisors, have per- 

 sistent pulps, and are consequently devoid 

 of true fangs, in which respect the Wom- 

 bat differs from all other Marsupials, and 

 resembles the extinct Toxodun, the denti- 

 eerous Bruta, and herbivorous Rodentia. 

 I may add that the Wombat deviates from 

 the other Marsupials in the number of its ribs; 

 as these are very constant in the rest of the order, 

 the difference in the Wombat, which has 15 

 pairs, instead of 13 or 12, is the more deserving 



* In all the placental Rodents, which have more 

 than three molars in each lateral series, the addi- 

 tional ones are placed at the anterior part of the 

 row, and are subject to displacement by a perma- 

 nent successor in the vertical direction, and conse- 

 quently are essentially " premolars," or spurious 

 molars ; the Wombat strikingly manifests its mar- 

 supial character in having four true molars on each 

 side of both jaws. 



