On the development and succession of the teeth in the Marsupialia : (abstract) / by William Henry Flower.

  • Flower, William Henry, 1831-1899.
Date:
1867
Catalogue details

Licence: Public Domain Mark

Credit: On the development and succession of the teeth in the Marsupialia : (abstract) / by William Henry Flower. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    4/4 (page 4)
    7 4 their habitual persistence throughout life, range them with the second or permanent series. We have been so long accustomed to look upon the second set of teeth as an after-development or derivative from the first, that it appears almost paradoxical to suggest that the milk- or deciduous teeth may rather be a set superadded to supply the temporary needs of mammals of more complex dental organization. But it should be remembered that, instead of there being any such relation between the permanent and the milk-teeth as that expressed by the terms “progeny” and “parent” (sometimes applied'to them), they are both (if all recent researches into their earlier development can be trusted) formed side by side from independent portions of the pri- mitive dental groove, and may rather be compared to twin brothers, one of which, destined for early functional activity, proceeds rapidly in its develop- ment, while the other makes little progress until the time approaches when it is called upon to take the place of its more precocious locum tenens. Many facts appear to point to the milk-teeth as being the less constant and important of the two sets developed in diphyodont dentition. Among these the most striking is the frequent occurrence of this set in a rudimen- tary and functionless or, as it were, partially developed state. The milk- premolars of some Rodents (as the Guinea-pig), shed while the animal is in uterOy the simple structure and evanescent nature of the milk-teeth of the Bats, Insectivores, and Seals, the diminutive first incisors of the Dugongs and Elephants, all appear to be cases in point. On the other hand, examples of the commencing or sketching out, as it were, of the successors to a well-formed, regular, and functional first set of teeth, are rarely, if ever, met with. Occasional instances of the habitual early deca- dence, or, perhaps, absence of some of the second or so-called permanent teeth occur in certain animals ; but these are rather examples of the disap- pearance or suppression of organs of which there is no need in the economy, and chiefly occur in isolated and highly modified members of groups in the other members of which the same phenomenon does not occur, as in Cheiromys among the Lemurs, Trichechus among the Seals, and the recent Elephants (as regards the premolars) among the Proboscideans. They form no parallel to the cases mentioned above of the rudimentary formation of an entire series of teeth of the temporary or milk-set. To return to the marsupials :—If this view be correct, I should be quite prepared to find, in phases of development earlier than those yet examined, some traces either of the papillary, follicular, or saccular stages of milk- predecessors to other of the teeth besides those determinate four in which, for some reason at present unexplained, they arrive at a more mature growth*. Such proof as this would alone decide the truth of these specu- lations ; and I have not at present either the requisite leisure or materials for following out so delicate an investigation. I trust that the facts already elicited are sufficiently novel and important to justify my bringing them, as they now stand, before the Society. * It may be remarked that the milk-tooth which alone is developed in the Marsu- pials corresponds homologically with that which, as a general rule, is most persistent in the typical diphyodonts, including Man, viz. the nosterior milk-molar, replaced by the posterior permanent premolar.