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.
25/614 (page 11)
![more pronounced grooves, or pits, which are pathological, and are marks of checks in development more or less com- plete. The enamel of some animals is, to all appearance, structureless ; such is the nature of the little caps which, like spear points, surmount tlie teeth of some fishes, and which from their extreme brittleness are often lost in pre- paring sections, so that their very existence has long been overlooked. Some of these enamel tips, however, present an appearance somewhat similar to the enamel of Sargus (p. 25). But the absence of structure, if such it really be, IS after all a mere question of degree : in the commonest ibrm of enamel, such as that of the human teeth, there is a finely fibrous structure, very apparent in imperfect teeth, but far less so in well-formed ones, and the enamel tips of fish are in the manner of their development, fibi'ous; so that even thougli we cannot distinguish its constituent fibres when it is completed, tliis is merely an indication that calci- fication has progressed a little farther than in human teeth : if calcification only goes far enough, all structure, if not de- stroyed, will at all events be masked from sight. The structure of human enamel has been stated to be filjrous; that is to say, it has a cleavage in a definite direction, and is capal)le of being broken up into fibres or prisms, which seem in transverse section to approximate more or less closely to hexagonal forms brought about by their mutual apposition. The ])risms run from tlic dentine towards the free surface ; this is, howevei, subject to many minor modifications. The curved and decussating course of the human enamel prisms renders it difficult to trace them tliroughout their length, ])ut tlie structure of the enamel of many lower animals (especially tlie rodents) is more easily intelligible. Enamel such as that of the Manatee, in which all the prisms pursue a perfectly straight course, is of com- paratively rare occurrence, but among the rodents the courses pursued by the enamel pi-isms are simple, and pro-](https://iiif.wellcomecollection.org/image/b21932025_0025.jp2/full/800%2C/0/default.jpg)
