Licence: Public Domain Mark
Credit: A system of dental surgery / by Sir John Tomes. Source: Wellcome Collection.
![the human subject. Hence, even these specimens may sei-ve to confirm the results obtained from an examination of healthy jaws so fiir as the teeth arc concerned. Those minor differences in size and form which constitute individuality, by which we are enabled to distinguish one ])crson from another, though in all essential charactei's they are precisely similar, must be borne in mind when investigations of this character are undertaken. It would perhaps be difficult to find a more interesting subject for investigation, than the progressive changes in form and of relative ja-oportion between the various parts of the jaws during infancy, which occur as necessaiy conse- ([uences of a mode of growth which is so subservient to the development and arrangement of the teeth. The fact that the development of the hard tissues of a tooth is preceded by the formation of soft tissues, or tooth- pTilp, of equal size and form to the futiire tooth, must at all times be kept in view. Not that the entire pulp assumes the dimensions of a perfected tooth before its conversion into tiic haixl tissue commences, but that cacli part of the gradually developing tooth is first formed in pulp tissue of its full size, and then calcifies. For example, the cusps of the molars and the edges of the front teeth first assume their full dimensions in the form of pulp, and then calcify; the l>rocess of gradual development and subsequent calcification ])r(>ceeding until the teeth are perfected. In dentine, which forms the great bulk of eacli tooth, we have no such thing as outward growth; no addition to the external surface of the formed tissue ever takes place, excepting by the superposition of the enamel, and of the cemeutum, which respectively coat the crown and the root of the tootli; l)ut these add compara- tively little to the size of the organ. Hence it follows that liotii the forms and dimensions of the crowns of the teeth are unalterably fixed long before the jaws are sufficiently enlarged to admit of their ultimate and normal ari-angement. If tlie maxilke of a nine months' fcutus be examined, it will be found that the union of the two halves both of the B 2](https://iiif.wellcomecollection.org/image/b21499081_0019.jp2/full/800%2C/0/default.jpg)
