Licence: Public Domain Mark
Credit: A manual of dental anatomy : human and comparative / by Charles S. Tomes. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
26/614 (page 12)
![duce very regular patterns, which are constant for particular families (J. Tomes). Thus, in the Sciuri<l<v, a section of the enamel, whether longitudinal or transverse, appears divided into an outer and inner portion, in which the prisms, although continuous from the dentine to the free surface, pursue different directions. As seen in longitudinal section, the enamel prisms start from the dentine at right angles to its surface, and after passing through about two-thirds of the thickness of the enamel in this direction, abruptly bend towards the tip, forming an angle of 4.5 degrees with their original course. In transverse section the enamel prisms are to be arranged in horizontal layers, each layer being a single found fibre in thickness; in alternate layers the prisms pass to the right and to the left, crossing those of the next layer at right angles, and thus making a pattern of squares in the inner two-thirds of the enamel. But in the outer third of the enamel, where the prisms bend abruptly upwards, those of superimposed layers no longer pass in opposite directions, l)ut are all parallel ; in fact no longer admit of distinction into alternate laminic. Thus each layer of enamel ])risms passes in a very definite direction and, seen with those of other layers, forms a very characteristic pattern ; but the enamel prisms are not inany part of their course curved. In the beaver the course of the j'l'isms is not quite so simple : to take the longitudinal section first, instead of the prisms starting off at right angles to the surface of the dentine, they are inclined upwards towards the a})ex of the tooth at an angle of GO degrees; then, after passing through about half the thickness of tiie enamel, they turn uji abruptly again, so that they are apjaroaching to parallelism with the dentine, here making in fact an angle a little less than 30 degrees with it. It follows from this that no transverse section can show very plainly the direction of tlie prisms in both parts of their](https://iiif.wellcomecollection.org/image/b21932025_0026.jp2/full/800%2C/0/default.jpg)
