PROFESSOR. OWEN OX THE EOSSIL MAMMALS OR AUSTRALIA. 
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in with a convexity lengthwise : in the latifront and other living species the bone is 
here concave in the direction of the skull’s axis. As the maxillary in Phascolomys 
macjnus proceeds to join the premaxillary, the convexity changes to a concavity, in which 
remains of the maxillo-premaxillary suture may be traced. 
The diastemal border (ib. fig. 2, 21 ') rises as it advances from the molar alveoli at a less 
open angle than in Phascolomys medius, in which, as in the recent species, it extends 
forward nearly on the same parallel with the line of the alveolar outlets. 
A shallow channel marks the inner surface of the commencement of the diastemal 
border (ib. fig. 1, 21 '), its course being from above obliquely forward; there is a feeble 
rising of the surface anterior thereto. The palate between the ridges is regularly arched, 
the span being 1 inch 6 lines, the depth or height of the arch 1 inch. The extent 
preserved just reaches the place of entry of the prepalatal or “ incisive” foramina, showing 
from the nasal cavity the hind wall of those canals and the increased vertical extent of 
the free inner surface of the premaxillary, making the sudden deepening of this part of 
the palate when viewed from below in such specimens as have that part entire, such as 
the subjects of fig. 2, Plate XXXII., & fig. 2, Plate XXXIII. a, from the smaller extinct 
species, Phascolomys medius. 
The fractured surface of the premaxillaries (Plate XXXV. fig. 5) exposes the incisors 
near the apical end of the long pulp-cavity, about 1 inch 3 lines above the diastemal 
ridge : the premaxillary increases in thickness as it rises to form the alveolus. The upper 
fractured surface of the present fossil (Plate XXXV. fig. 4) exposes part of the floor of 
the nasal passages, gradually descending as they retrograde toward the place of the post- 
palatine apertures. Most of the intermolar floor of these passages and roof of the mouth 
has been broken away. 
On each side of the nasal passages appear the hollow implanted ends of the molar 
teeth. That of d 3 (fig. 4) projects above the prezygomatic ridge, that of d 4 between 
this and the front pier of the zygoma ( 21 *) ; and the relative position of the rest 
conforms with the generic type of these singular elongate, outwardly curved, ever- 
growing teeth. 
The total length of the first and smallest, following the curve, is 2 inches 9 lines. 
The long diameter of the oval or subtriangular grinding-surface is 6 lines ; the breadth 
near the base, which is backward, is 5 lines. The inner enamelled side extends forward, 
with a very slight outward bend, from the axial line of the skull to the apex, which is 
narrow and obtuse, and round this the enamel bends for a short way along the outer 
side of the tooth ; this is the longest side, and curves from behind forward and inward 
to the apex more strongly than does the inner side. The enamel can be traced from the 
inner side over the greater part of the hind surface of the tooth. The coat of cement 
covering the outer side of the tooth can be traced over parts of the enamel, the whole 
of which it seems originally to have covered. 
The grinding-surface of the second molar (d 4) gives 9 lines in fore-and-aft diameter, 
6 lines across the hinder lobe ; that of the third molar (m 1 ) has the same longitudinal 
