330 MR. OWEN ON THE CLASSIFICATION 
jaw inwards. ‘The false and true molars, like the incisors, have persistent pulps, and 
are consequently devoid of true fangs: in which respect the Wombat differs from all 
other Marsupials, and resembles the extinct Toxodon, the dentigerous Bruta, and her- 
bivorous Rodentia. 
Although none of the Marsupialia possess teeth composed of an intermixture of layers 
of ivory, cement and enamel through the body of the crown; yet the layer of cement 
which covers the enameled crown is thickest in the vegetable-feeding Marsupials, and is 
remarkably distinct in the Wombat. 
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 of notice. The Koala, 
like the Phalangers and Kangaroos, has 13 pairs of ribs. 
A few words, in conclusion, as to the claims of the Marsupialia to be regarded as a 
natural association. It may be admitted, that at the period when that most judicious 
and learned naturalist, the then Vice-Secretary of the Zoological Society, published his 
reasons for rejecting the Marsupialia as a distinct group in the ‘Systema Mammalium’,’ 
and for distributing them among different placental orders, according to their supposed 
closer affinities, the contrary views set forth by M. De Blainville were defective in that 
kind of evidence which could alone render them convincing. The organization of the 
Marsupial animals was not at that time sufficiently elucidated to render any opinion as 
to their natural affinities really valid. Subsequent dissections have, however, shown 
that the hypothesis which Cuvier had sanctioned by his authority was correct. The 
Marsupial animals have been proved to agree among themselves, and to differ from 
the analogous placental species by several important organic modifications not suspected 
when the Mammalia in the Museum of the Zoological Society were arranged according 
to the Quinary System. 
I have shown that in their cerebral conformation the Marsupialia manifest a close 
correspondence with the Ovipara in the rudimental state of the corpus callosum: the dif- 
ference which the most closely analogous placental species offer in this respect is broadly 
marked®. The correspondence of the Marsupials with each other is not less constant 
in the structure of the heart, of which the right auricle manifests no trace of a fossa 
ovalis and annulus ovalis, and receives the two vene cave superiores by two separate in- 
1 «Gardens and Menagerie of the Zoological Society delineated,’ vol. i. p. 265. 
2 Mr. Bennett asks in 1831, “‘ What is there of importance in the structure of the Wombat except this soli- 
tary character of the maisupium to separate it from the Rodent Order?” We may now suggest, in reply, the 
marsupial number of true molar teeth, the transverse condyle of the lower jaw, the rotatory muscle of the hind- 
foot,—important in the present question on account of its frequency in the marsupial species, to which it is 
peculiar ; and, besides other characters, I would more particularly refer to the difference in the structure of the 
brains of the Wombat and Beaver, described in the Phil. Trans, 1837, p. 89, pl. vi. figg. 3 and 4. 
