50 OREODON. 
internal, and least so upon that postero-internal. Of the first true molar the inner 
half alone is preserved, and presents the corresponding lobes with broad crescentic 
surfaces of dentine. 
The socket of the fourth premolar had lost its tooth, and is now filled with 
matrix. 
Portions of the crowns of the third and second premolars, yet remaining, indicate 
that these teeth had not been protruded from the gums. 
From this account, it appears that all the permanent true molars are fully pro- 
truded before the temporary molars are shed. 
The two entire teeth above indicated, are in this specimen a trifling degree 
smaller than in specimens 1 and 10, and yet the fragment of skull, though not of a 
fully adult animal, is larger than the corresponding portion of any of the preceding 
specimens described. In the upper view, it appears as if it had belonged to a 
distinct species from Oreodon Culbertsonii, and had it been the only specimen in 
the collection besides the first indicated in the list, I would have so considered it 
without hesitation, but, from the many variations presented in numerous individual 
cases, I am inclined to think it is only a variety. 
The forehead is unusually long and broad; being about three-fourths of an inch 
ereater in the former direction than in the largest specimen previously indicated. 
The supra-orbitar foramina are removed to double their usual distance from the 
fronto-nasal suture, or rather they appear to occupy the ordinary position, while 
the portion of the os frontis in advance of them is unusually prolonged. The 
lachrymal depression, also, is more shallow than usual, apparently by the spread- 
ing or expansion of the lachrymal bone; for the outer face of this is several lines 
higher and broader than in the preceding specimens. 
From the collection of Dr. Owen. 
e MEASUREMENTS. 
: Inches. Lines. 
Distance of infra-orbitar foramina from frontal angular processes. 3 oat: 6 
Distance of supra-orbitar foramina from fronto-nasal suture. . : aaa tes! ! 2 
Length of series of upper true molars : : é : 5 é etre 9 
Antero-posterior diameter of last molar 3 * 3 . : : : 8 
14. A fragment of a face of a young animal, containing on both sides portions 
of the temporary molars; the succeeding two permanent true molars; and, con- 
cealed within the jaw, the last molar. 
From the collection of Dr. Owen. 
15. The greater portion of a face and lower jaw, containing all the molars 
except one of both sides. It presents nothing peculiar, except a slight variation 
in details of size. 
From the collection of Dr. Owen. 
