On the origin and development of the pulps and sacs of the human teeth / by John Goodsir.

  • Goodsir, John, 1814-1867.
Date:
[1839]
Catalogue details

Licence: Public Domain Mark

Credit: On the origin and development of the pulps and sacs of the human teeth / by John Goodsir. Source: Wellcome Collection.

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    responding with a tubercle ; while their edges correspond with the grooves on the grinding surfaces of these teeth.* The inner lip of the dental groove (or the outer edge of the palate) which has been increasing for some time past, is now at the fourteenth week, so large as to meet and to apply itself in a valvular manner to the outer lip or ridge, which has also been in¬ creasing, The follicles at this time grow faster than the papillae, so that the latter recede into the former. The molar papillae gra¬ dually acquire two or three additional small compressed tubercles on their sides, and their apices become less conical, so that they still more resemble the molar teeth of the carnivorous mammals.f The opercula of the follicles continue to increase, so as almost to hide their contained papillae. The primitive dental groove, which at this period contains ten papillae in as many follicles, and is situated on a higherlevel than at first, may be now more properly denominated the secondary den¬ tal groove. It is when in its secondary condition that the groove affords a provision for the production of all the permanent teeth, with the exception of the first or anterior molars. It is about the fourteenth or fifteenth week that we begin to observe prepara¬ tions made for this provision, by the gradual appearance of a little depression in the form of a crescent, immediately behind the in¬ ner opercula of each of the milk tooth follicles. The concave edges of these depressions are in contact with the attached mar¬ gins of these opercula. Those of the centre incisives appear first, then the laterals, canines, anterior bicuspids, posterior bicuspids. About this time the opercula close the mouths of the follicles, but without adhering, then the anterior closing first, the laterals, and so on in succession.^ The lips and walls of the secondary groove now begin to cohere m a direction from behind forwards, the opercula and every part of the groove, with the exception of the ten de¬ pressions for the permanent teeth, becoming rough, flocculent, and adherent. The follicles have now become the sacs ; the papilla? * It would be interesting to ascertain whether the opercula of the human tooth follicles may not be rudimentary organs, which are to attain their utmost develope¬ ment in the sacs of the elephantoid, ruminant, and other compound teeth, under the form of depending folds lor the secretion of the intersecting enamel and cement plates. One may easily conceive the mode of formation of a composite tooth sac, hy sup¬ posing the opercula, after their edges have met, to dip down back to back between the divisions of the pulp, till they almost meet the common body of the latter. -j- This is another instance of the law of progressive developement, by virtue of which an organ, in the course of its formation, passes through phases, which correspond to permanent conditions of the same organ in other animals. A human molar tooth pulp is at first rounded, as in certain fishes ; then conical, as in other fishes and rep¬ tiles ; then conical, but flattened transversely, gradually acquiring two or more ad¬ ditional conical tubercles, as in the carnivorous mammals ; and finally, by the equa¬ lization of the primary and secondary tubercles, asssuming the shape of the mo¬ lars in the quadrumanous animals and man. In the elephantoid, ruminant, and rodent animals, it probably undergoes a further and ultimate change in the deepen¬ ing of the rudimentary grooves on the grinding surface.