270 
PIIAL A NO I ST A URSIXA. 
also in the Museum, I lcam tlmt the principal premolar tootli 
is developed at a relatively earlier period than in the Hypsi- 
prymni, it being more advanced, in the skull in question, than 
the third true molar. In the Rat-Kangaroos, as I have before 
noticed, it is the last tooth to make its appearance. 
The bones of the skull of P. ursina are much thicker and 
stronger than in the P. vulpina; the muzzle is propor¬ 
tionately shorter and broader; the zygomatic arch deeper. 
The nasal bones are dilated at each extremity, where their 
width is the same, or very nearly so. The rami of the lower 
jaw are considerably deeper than in the P. vulpina , and die 
symphysis menti forms a more obtuse angle; and, in con¬ 
nection with this diiierenco in the angle formed by the sym¬ 
physis, we find the lower incisor teeth directed more upwards. 
All the teeth are larger in proportion than in P. vulpina , and 
in the relative proportions of certain teeth there are differences: 
thus the anterior upper two incisors are longer in proportion 
to the other two pairs, and the principal premdlar is larger in 
proportion to the true molars, being equal in length, and 
nearly equal in width, to the foremost true molar. The {Ulte¬ 
rior margin of the post-palatine opening is on a line with the 
middle of the first true molar. 
The adult skull, according to M. Temminek's figure, is 
four inches and one line in length, and two and a half inches 
in width. The two skulls alluded to as being in the British 
Museum collection yield the subjoined dimensions: those in 
the first column are from a nearly adult skull; those in the 
second are from the skull of a young animal, in which 
only two of the true molars are perfectly developed: in both 
skulls there are two small teeth immediately behind the 
lower incisor, the foremost of which, 1 suspect, represents the 
lower canine:— 
