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Show 1896.1 MAMMALIAN DENTITION. 583 set which terminates the series. This is borne out by the discovery by numerous authors (5, 7, 9, 20) of a lingual growth of the dental lamina by the side of the germs of the permanent teeth. Pig. 1. Pig. 2. Fig. 1.-Diagram of the tooth-succession in a polyphyodont Reptile : 1, 2, 3, successive tooth-germs ; d.l, dental lamina. Fig. 2.-Diagram illustrating the relation of a molar tooth-germ (m) to the dental lamina (d.l). Taking the above into consideration, the presence of true and definite outgrowths from the dental lamina nearer the gum than and thus labial to the molar germs is extremely interesting and suggests that possibly at least one set of teeth preceding the functional molars has been suppressed. These vestiges are, it is true, minute and variable, but when compared with the obvious vestiges of the anterior milk-teeth seen in Erinaceus it does seem rash to conclude that these labial growths in the molar region are the last indications of an earlier set of teeth. If this is the case, then the molar teeth are not to be referred to the 1st, but rather to the 2nd dentition. The question then arises, is the milk-dentition the 1st set of teeth? This has been answered in the negative by Leche, and I hope shortly to publish a further confirmation of this view. Leche (7 a) has discovered in the anterior region of the jaw of Myrmecobius a minute set of teeth which precede the functional set; and as the latter set are now? usually regarded as the milk-dentition, this vestigial series is termed the pre-milk series, and may be compared with those small embryonic teeth seen in the Crocodile (19 a) and Iguana (8) \ 1 Rose ("Das Zahnsystem der Wirbeltiere," Ergebnisse d. Anatomie u. Ent-wickelungsges., 1894) refers to traces of a pre-milk dentition in M a n and suggests even an earlier set of teeth in the Vertebrata, a remnant of the placoid tooth-papilla, describing in all 5 sets, traces of at least four of which are found in the Mammalia. |