44 OREODON. 
we adopt a hypothesis which supposes the lateral incisors of Oreodon to be trans- 
formed canines, and the functional canines to be the transformed first of the 
normal series of seven molars. The latter view is favored by the absence in 
Oreodon of the first of the normal number of molars, and also by the unusual 
position of the inferior canine tooth. Further, the latter has almost the exact form 
which would be produced by merely prolonging the crown of the first functional 
premolar. On the other hand, in Paleotherium, the lower and upper canines have 
the same relative position as in Oreodon, and yet the lower jaw has the normal 
number of premolars. j 
Temporary Dentition and Order of Succession—The deciduous dentition of 
Oreodon, so far as can be ascertained from the specimens under investigation, is 
expressed by the following formula :— 
ave anc p.m. i Fleas 
A EF RS Re) eet | 
In the order of protrusion of the temporary molars, judging from the relative 
extent of abrasion which these teeth have undergone in the specimens under 
observation, the true molar is first, and then follow the premolars in succession 
from behind forward. 
Form of the Temporary Molars.—(P1. IV. Figs. 4,5; V. 2,3; VI. 6, 7, 10, 11.) 
The superior temporary true molar has exactly the same form as the permanent 
true molars, but is about one-sixth less in size than the first of these. (V. 2, 3.) 
The crown of the second upper premolar is composed of three lobes like those 
of the true molars: two posterior and transverse, the other anterior and opposite 
to them. It resembles very much the crown of the fourth permanent premolar in 
conjunction with that of a small third premolar. The anterior lobe at its inner side 
is connected with the adjacent side of the postero-internal lobe by means of a 
shallow fold, which forms a cul-de-sac between the two. 
The anterior premolar has nearly the same form as the corresponding permanent 
tooth, but is smaller in size. Its antero-internal culs-de-sac are not as deep as in 
the latter, and the external of these is twice as broad as the other, but is shallower. 
The inferior deciduous true molar, as in all existing ruminants, possesses three 
pairs of symmetrical lobes, which have the same form, and the same relative posi- 
tion with one another as those of the permanent true molars, but which decrease 
in size from behind forward. (IV. 4,5; VI. 6, 7, 10, 11.) 
The two deciduous premolars of the lower jaw closely resemble in form the 
corresponding permanent teeth. ; 
The normal first superior molar appears to belong to the permanent series, 
succeeds all the temporary molars in the order of protrusion, and has no deciduous 
predecessor. 
The permanent true molars successively protrude and occupy their functional 
position before any of the deciduous molars are shed. The displacement of the 
latter by their permanent successors, appears to begin with the eruption of the 
last of these, which is followed by those in advance. The first permanent 
premolar of the upper jaw appears to have protruded after the deciduous teeth, 
