Had Cuvier been guided in his determina tions of the teeth by their mutual opposition in the closed mouth, and had studied them with this view in the Carnivora, with the dentition most nearly approaching to the typical formula, viz. the bear, he could then have seen that the three small and inconstant lower premolars (p. 1, p. 2, p. 3) were the homotypes of the three small and similarly inconstant premolars above; that the fourth false molar (p. 4) below, which, as he observes, " alone has the normal form," * was truly the homotype of the tooth above (p. 4), which he found himself com pelled to reject from the class of " fausses molaires," notwithstanding it presented their normal form; that the tubercular tooth, vs. I, which he calls " carnassiere " in the lower jaw, was the veritable homotype of his first " molaire tuberculeuse " above (m. 1), and that the tooth in the inferior series which had no answerable one above was his second " tuber culeuse" (my m. 3), and not any of the four false molars. The true second tuber cular above (m. 2) is, however, so much de veloped in the bear as to oppose both m. 2 and N. 3 in the lower jaw, and it might seem to 5nclude the homotypes of both those teeth coalesced. One sees with an interest such as only these homological researches could ex cite, that they were distinctly developed in the ancient Amphieyon (fig. 576.), which ac cordingly presents the typical formula. Thus, I repeat, the study of the relative position of the teeth of the bear might have led to the recognition of their real nature and homolo gies, and have helped to raise the mask of their extreme formal modifications, by which they are adapted to the habits of the more blood thirsty Carnivora. But the truth is plainly and satisfactorily revealed when we come to trace the course of development and succes sion of these teeth. The weight which must ever attach itself to an opinion sanctioned by the authority of both the Cuviers, demands that a conclusion contrary to theirs, and which seems to be opposed by Nature herself in certain instances, should be supported by all the evidence of which such conclusion is susceptible.
I proceed, therefore, to show how, in the bear, my determinations of the teeth are es tablished by their development, as well as by their relative position. As the question only concerns the molar series, the remarks will be confined to these. In the jaws of the young bear, figured in cut 581., the first premolar, p.1, is the only one of the permanent series in place; similarity to p. 4 in the lower jaw (fig. 581, nuns), to be veritably the last of the pre molar series, and to agree not in shape only, but in every essential character, with the three preceding teeth called by Cuvier " fausses molaires." So, likewise, in the lower jaw, we see that the primitive deciduous series, d. 1, d. 2, d. 3, and d. 4, will be displaced by the corresponding premolars,p. 1,p. 2, p. 3, and p. 1 ; and that the tooth nz. 1, called car nassiere by Cuvier, in the lower jaw, differs essentially from that p. 4, so called in the upper jaw by being developed without any vertical predecessor or deciduous tooth.
The same law of development and succes sion prevails in the genus Canis (fig. 582.). Although the tooth m. 1 in the lower jaw has exchanged the tubercular for the carnassial form, it is still developed, as in the bear, behind the deciduous series, and indepen dently of any vertical predecessor ; and the tooth p. 4 above, although acquiring a relative superiority of size to its homologue in the bear, and more decidedly a carnassial form, is not the homotype of the permanent carnas sial below, but of that premolar (p. 4) which is destined to displace the deciduous carnassial d. 4. The symbols sufficiently indicate the relations of the other teeth, and the conclu sions that are to be drawn from them as to their homologies. It is interesting to observe in the deciduous, as well as in the permanent series, that the lower carnassial d. 4 is not the homotype of the upper one d. 3, but of the
tooth which Cuvier calls the " tuberculeuse du lait," d. 4 in the upper jaw.
the other grinders in use are the deciduous molars, d. 2, d. 3, and d. 4; d. 2 will be displaced by p. 2, d. 3 by p. 3, and d. 4 by the tooth p. 4, which, notwithstanding its size and shape, Cuvier felt himself compelled to discard from the series of false molars, but which we now see is proved by its developmental relations to d. 4, as well as by its relative position and In the genus Fells (fig. 580.), the small per manent tubercular molar of the upper jaw, m. 1, has cut the gum before its analogue d. 4 of the deciduous series has been shed ; but though analogous in function, this is not ho mologous with, or the precedent tooth to in. 1, but, as in the dog, to the great carnassially modified premolar, p. 4. In the lower jaw the tooth (m. 1), which is functionally analogous to the carnassial above, is also, as in the dog, the tition, are M. 2 in the upper jaw, nz. 2 and ?it. 3 in the lower jaw ; p. 1 in the upper jaw, p. 1 first of the true molar series, and the homo type of the little tubercular tooth (nt. 1) above. And the homologies of the permanent teeth p. 4 above and nt. 1 below, with those so and p. 2 in the lower jaw ; thus illustrating the rule enuntiated above, that, when the molar series falls short of the typical number it is from the two extremes of such series that the symbolised in the dog (fig. 582.), teach us that the teeth which are wanting; in order to equal the number of those in the canine den teeth are taken, and that so much of the series as is retained is thus preserved unbroken. In the great extinct sabre-toothed tiger (lila chairodus, fig. 580, VI #), the series is still ther reduced by the loss ofp. 2 in the upper jaw.
That the student may test for himself the demonstration which the developmental cha racters above defined, yield of the true nature and homologies of the feline dentition,— the most modified of all in the terrestrial Carnivora, he is recommended to compare with nature the following details of the appearance and formation of the teeth in the common cat. In this species the deciduous incisors d. i. begin to appear between two and three weeks old ; the canines d. c. next, and then the molars d. follow, the whole being in place before the sixth week. After the seventh month they begin to fall in the same order ; but the lower sectorial molar M. 1, and its tubercular homo type above (m.1) appear before d. 2,d. 3, and d. 4 fall. The longitudinal grooves are very faintly marked in the deciduous canines. The first deciduous molar (d. 2), in the upper jaw is a very small and simple one-fanged tooth ; it is succeeded by the corresponding tooth of the permanent series, which answers to the second premolar ( p. 2) of the hyxna and dog. The second deciduous molar (d. 3) is the sectorial tooth ; its blade is trilobate, but both the anterior and posterior smaller lobes are notched, and the internal tubercle, which is relatively larger than in the permanent sectorial, is continued from the base of the middle lobe, as in the deciduous sectorial of the dog and hymna ; it thus typifies the form of the upper sectorial, which is retained in the permanent dentition of several Viverrine and Musteline species. The third or internal fang of the deciduous sectorial is continued from the inner tubercle, and is opposite the interspace of the two outer fangs. The Musteline type is further adhered to by the young Feline in the large proportional size of its deciduous tubercular tooth, d. 4. In the lower jaw, the first milk molar (d. 3) is succeeded by a tooth (p.3) which answers to the third lower premolar in the dog and civet. The deciduous sectorial (d. 4), which is succeeded by the premolar (p. 4), an swering to the fourth in the dog, has a smaller proportional anterior lobe, and a larger pos terior talon, which is usually notched ; thereby approaching the form of the permanent lower sectorial tooth in the Mustelido.