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Show 1896.] MAMMALIAN DENTITION. 577 successional teeth, shows conclusively to my mind that the first premolar is present as a calcified tooth in one dentition only, viz., in the milk-dentition ; the milk-tooth (jjLf i) being very large and persisting in the adult along with the permanent teeth, a slight trace only of its successor being visible at a very early stage and only for a short period. I must further conclude that the teeth figured by Bate as ^-r have no existence, his '.. being in reality persistent milk-teeth. I can only imagine that Bate was misled by the presence of the small needle-like teeth seen in connection with all the other ante-molars into the belief that he had lost a similar one in connection with P-^r during dissection. pm 1 ° Leche, while accepting Bate's account, which he was bound to do from the limited material at his disposal, states that pm. 1 was much more backward than the other milk-teeth, for while the latter had well differentiated enamel-organs, that belonging to pm. 1 was still club-shaped or only slightly advanced. Thus his specimens form with mine a perfect series, which together show that at no time is there more than one representative of pm. 1 differentiated as a tooth, i. e. dpm. 1, and only for a short period is there any indication of ppm. 1. General Consideration of the Homology o/Pm. 1. Although there is undoubtedly but one calcified representative of pm. 1 present in the Mole, it is possible that some may be inclined to regard that tooth as belonging to the permanent rather than to the milk series ; in that case the lingual growth of the dental lamina would have to be regarded as the representative of the post-permanent series, similar to that seen in connection with the permanent incisors and canines (fig. 28, pc. dl.). Such an interpretation has been adopted by Tims (24) for pm. 1 of the Dog and Pig1, this author further stating his belief that in those cases (Hyrax, &c.) in which pm. 1 is duplicated, the two teeth represent the permanent and post-permanent series, and not the milk and permanent sets as one might suppose them to do. Against this possible interpretation of pm. 1 in the Mole may be urged in 1 With regard to Tims's description of the 1st premolar of the Pig, in which he figures traces of three dentitions, I believe that, there has been a mistake in the identification of the teeth, for which I a m partially responsible, the sections and rough identification of the teeth being mine. O n making a fresh and more careful examination of the sections, and comparing them with an older specimen, I find a very backward tooth-germ present between the canine and the supposed 1st premolar: this backward germ I take to be the true pm. 1, the tooth figured by Tims being dpm. 2 ; in that case the enormous development and swollen nature of the lingual growth of the dental lamina is accounted for, it being the germ of ppm. 2, while the labial growth must represent a trace of the pre-milk dentition. |