Atlas and text-book of dentistry including diseases of the mouth / by Gustav Preiswerk. Edited by George W. Warren.

  • Preiswerk, Gustav
Date:
1906
Catalogue details

Licence: Public Domain Mark

Credit: Atlas and text-book of dentistry including diseases of the mouth / by Gustav Preiswerk. Edited by George W. Warren. Source: Wellcome Collection.

Provider: This material has been provided by the University of Toronto, Harry A Abbott Dentistry Library, through the Medical Heritage Library. The original may be consulted at the Harry A Abbott Dentistry Library, University of Toronto.

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    According to Baunie the shortening of the jaw bone in the conrse of evolution forces the niilic teeth out of the tooth row. He considers, therefore, the milk teeth as a part of the permanent set, the difference being only one of time. Other authorities also believe that the diphyodont type, that is having a milk and a permanent set of teeth, develops from the monophyodont type and that this occurs only in the mammals. In Zittel's opinion, with which I agree, it has not been proven that the diphyodont mammals are developed from the monophyodont, for on the contrary many monophy- odont types are known whose predecessors possessed two sets of teeth. As examples we need only to mention the proboscidea, many of the rodents, the insectivora and the edentata, in all of whom the shedding of the milk teeth is evidently a retrogressive process in comparison with that of their ancestors. According to the imjjortant con- tributions of Kiickenthals the embryos of monophyodont mammals very often possess milk tooth germs which, however, never reach development or eruption. Other observers, among them Kollmann, have noticed the same occurrence in man. In this case it is supposed that the tooth ledge produces supernumerary milk tooth germs which, however, only occasionally develop into supernu- merary teeth. We hold a convincing argument against Bannie's theory, if it is concluded from the above state- ments and from the observation of Kiitimeyers that the milk teeth inherit the evolutionary forms of their ancestors and what seems most plausible that the monophyodont forms descend from the diphyodont and perhaps the diphyodont from polyphyodont. Therefore, from the ]ier- petual sluMlding of milk teeth, which for example is tv])ical in the shark, the diphvodont type develo]>s and from it the monojdiyodont type. Through differentiation and perhaps occasional retrogression in the development of the individual tooth it a]ipears that tlie number of sets of teeth become constantly small(>r. At first simple teeth were supj)lied which were continually sIkmI, then when the type of the teeth IxH'ame more complex nature became
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