153 



This characteristic form of the penultimate upper inilk 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 Hi/opoiamiis, 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 Hyopotamits 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 \\e\N 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: "On reconnait aiscment la 

 seconde de lait pour ce qu'elle est, a sa forme allongee, a ses trois paires de crois- 

 sans, et a son appendice transverse place avant les croissans." — Dpiuv " paires de 

 croissans " would have been more correct. The possibility of an error in relation 



