153 
This characteristic form of the penultimate upper milk tooth, 
namely the want of the inner crescent of the anterior pair, with the 
presence of the additional cusp in front, plainly marks as this tooth, 
that which Prof. Owen has indicated as the penultimate premolar in 
his recently discovered genus Hyopotamus, and as the last premolar 
in his also newly-described genus Dichodon; the tooth behind it in 
each case being the last milk tooth, which always agrees exactly with 
the true molars, but is distinguishable from them by its suddenly 
diminished size. The series of upper molars of the latter animal 
have been placed, in the published figure, to the extent of one tooth 
too far back ; were they brought forward to their true position, the 
tripartite tooth below, which, according to all laws of form and suc- 
cession, can be no other than the last milk molar, (of which the suc- 
cessor has not begun to appear,) would antagonize by its anterior 
pair of crescents with the space in front of the posterior pair in the 
penultimate milk tooth above. Of the Hyopotamus Vectianus, the 
figure represents a series of the crowns of five upper molars, of which 
the first is, as I have before observed, manifestly a penultimate milk 
tooth. These being represented without any appended portion of 
jaw, and no mention being made in the text as to whether they were 
found connected, it seems rather probable that such was not the case, 
and in the side view roots are added in outline to certain of the teeth 
and not to others, which makes that matter still more doubtful. At 
all events, this condition of things could not possibly have co-existed 
with that represented in the lower jaw attributed to the same species ; 
since in the upper series of teeth we may count ten principal trans- 
verse eminences, while in the lower series of five molars, which ought 
to fit them, there are only eight depressions : besides which, it is im- 
possible that the elevated summits presented by the trenchant lower 
premolars, with the correspondingly deep notch which their interval 
affords, could ever fit the comparatively diminutive elevations and 
depressions presented by the foremost teeth above. The lower true 
molars, however, show a much more worn condition than the upper 
ones ; but even if it should be possible that the series of upper molars 
represented were in place and in use at the same time, it is evident 
that the foremost of them cannot be premolars *. 
* I do not claim to be the sole discoverer of these incongruities (apparently 
the results of a too hasty determination), since I am aware that the true nature 
of the tripartite inferior tooth in the Dichodon has been perceived by some emi- 
nent comparative anatomists and naturalists; but I am here compelled to attempt 
their refutation, since, were Prof. Owen’s determinations in these instances cor- 
rect, insuperable objections would be presented to my generalizations on the cha- 
racter of the premolars as distinguishing the two groups of Ungulate Mammalia, 
and on that of the penultimate upper milk tooth as indicative both of its position 
in the series, and of the affinities of certain genera. 
That the character of the penultimate upper milk tooth was appreciated by Cu- 
vier, will appear from a passage in the ‘Ossemens Fossiles,’ although it is rather 
vaguely and not quite correctly described. In speaking of a fragment of the upper 
jaw of a deer from the breccia at Nice, he observes: “(Qn reconnait aisément la 
seconde de lait pour ce qu’elle est, A sa forme allongée, a ses trois paires de crois- 
sans, et A son appendice transverse placé avant les croissans.”—Deusx “ paires de 
eroissans” would have been more correct. The possibility of an error in relation 
