A hand-book to the marsupialia and monotremata / by Richard Lydekker.

  • Lydekker, Richard, 1849-1915.
Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: A hand-book to the marsupialia and monotremata / by Richard Lydekker. Source: Wellcome Collection.

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    in their development, although the hinder pair are invariably the larger of the two, and form the chief agents in progres- sion ; the greatest development of the hind limbs occurring among the Kangaroos. As a rule, there is a well-developed tail, this appendage being generally long and tapering, in some cases prehensile, and at others forming an additional support to the body. Great variation obtains in regard to the form and number of the teeth, which may be adapted either for a carnivorous, insectivorous, or herbivorous diet, although they are always divided into incisors, canines, premolars, and molars. There is, however, a marked peculiarity in regard to the succession of the teeth, which may be considered as characteristic of the order. Thus, instead of the whole, or nearly the whole of the first set of teeth in advance of the true molars or hindmost cheek-teeth, being replaced by a second set of permanent teeth, only one tooth is thus replaced, and that not invariably so. The tooth thus replaced has been hitherto generally regarded as corresponding to the last or fourth milk- molar of the higher Mammals, while the apparently replacing tooth has consequently been identified with the last or fourth premolar of the same. Recent researches have, however, tended to show that this is not a true case of replacement at all, and that the tooth which makes its appearance late in life is really a retarded premolar, which will consequently be the fourth of the full series, while the apparently replaced tooth is really the fifth. Be this as it may, the mode of succession is peculiar and unique ; and it may be still convenient to speak of the replacing tooth as the fourth premolar, and the one it displaces as the fourth milk-molar. It is worthy of mention, as an admirable instance of adaptation to peculiar conditions, that during the period while the helpless young are adherent to the teats of their parents their breathing organs are specially modified in order to prevent the danger of choking by the