PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
257 
appear in m 3. The proportion of length to breadth of the grinding-surface of the true 
molars is the same in the recent as in the extinct species compared ; the difference is 
mainly in size. 
In a portion of the right mandibular ramus of Macropus Titan , with the three pos- 
terior molars in situ , these, like the single entire molar in Plate XXII. fig. 17, m 1 , show 
a proportionally greater antero-posterior extent of the prebasal ridge than in Macropus 
major or Macropus ( Osphranter ) rufus. Of the latter existing species* Mr. Gould, 
F.R.S., was so good as to place in, my hands, for the purpose of these comparisons, the 
jaws and teeth of a male which he killed between the rivers Murray and Adelaide, 
Australia ; it measured 8 feet 2 inches from the nose to the end of the tail, and was 
the largest Kangaroo which that eminent naturalist saw in the continent of which he 
has so admirably illustrated the rich ornithology as well as its singular mammalogy. 
These specimens I presented, in Mr. Gould’s name, to the Royal College of Surgeons^, 
after their application to the requisite comparisons with the fossils from the Wellington 
Valley caves and freshwater beds of Australia. Figs. 1 & 14 in Plate XXIII. give a 
side view, and figs. 2 & 4, Plate XXI. the grinding-surface, of the right series of upper 
and lower molars of this animal, of the natural size. 
So much of the mandibular ramus of a M,acropus Titan (Plate XXII. figs. 13-16) as 
remains in the specimen in the Oxford Museum closely agrees, save in size, with that of 
Macropus major (Plate XX. fig. 15). As in that recent specimen, the individual affording 
the present fossilized relic had shed both the premolar and the two anterior milk-teeth ; 
d 4 also shows a wear of crown and exposure of roots indicative of speedy expulsion. 
The long diastemal border (between d 4 and i) is trenchant to near the outlet of the 
incisive alveolus. It descends, more rapidly than in the living Kangaroo, from the 
anterior molar socket, with a concave curve, reducing the vertical extent of the sym- 
physial part of the ramus at the outlet of the dental canal (ib. fig. 13, v ) to two thirds 
of that at the outlet of the anterior molar socket, d 4. In advance of the dental canal 
the symphysial part of the jaw is reduced to a mere case of the root of the long pro- 
cumbent incisor, i. 
The descent is less sudden, and the concavity of the diastemal border somewhat less, 
in another specimen of the mandible of Macropus Titan , which more closely resembles 
in this respect the recent Kangaroo. 
The symphysial surface in Macropus Titan (Plate XXII. fig. 15) begins behind, in 
advance of the vertical parallel of the fore part of the first molar socket ; it expands so 
as to cover the lower half of the inner surface of the ramus at the part opposite the 
outlet ( v ), and then contracts to terminate before attaining the outlet of the incisive 
alveolus, at least as regards its grooving and other rough markings for ligamentous 
union. The contrast between this structure of the symphysial joint and that in fig. 6, s 
(Sthenurus Atlas), is considerable, and supports the inference that the junction between 
* Then, known as the Macropus laniger. 
t See ‘ Catalogue of the Fossil Mammals and Birds ’ &c., 4to, 1845, pp. 324, 325, Nos. 1510, 1511. 
