The microscopic anatomy of the teeth / by J. Howard Mummery.

  • Mummery, J. Howard (John Howard), 1847-1926.
Date:
1919
Catalogue details

Licence: In copyright

Credit: The microscopic anatomy of the teeth / by J. Howard Mummery. Source: Wellcome Collection.

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    structure to their several purposes ; the pointed, more or less conical teeth being employed for the seizure of prey, both the sharp pointed teeth of many fishes and the more powerful canines of Carnivora. The incisors are modified for dividing and tearing, and the molars both for this purpose, and also, in many animals, for the grinding and trituration of the food. In all these modifications they are most perfectly adapted to their chief purpose, the seizure and preparation of the food. As resisting power and a certain degree of hardness are essential to the functions performed by the teeth, they are usually calcified, that is, permeated by, or impregnated with, inorganic salts. Some teeth, however, persist through¬ out life as horny structures, produced from the stratum corneum of the oral epithelium, as the teeth of the Cyclo- stomata (Petromyzon, Myxine, and Bdellostoma) in fishes, and the adult structures in Ornithorhynchus which take the place of teeth, although more correctly described as horny plates. While confined in the higher forms to the maxillary, premaxillary, and mandibular bones, teeth are found, especially in fish, in many other positions, as on the pre- mandibular, vomer, pterygoid, and pharyngeal bones, and upon the branchial arches. In many fish the whole mouth bristles with teeth, and they are even found upon the tongue in the parasitic Myxine. Homy structures are also present on the tongue of Ornithorhynchus. Three chief tissues constitute the structure of the com¬ pleted tooth : dentine, enamel, and cement. The bulk of the tooth is made up of dentine, a hard calcified substance penetrated in different degrees by channels ; an exceedingly hard external layer, the enamel, is present in most teeth and covers the exposed surface of the crown and the roots, and in some instances the crowns of the tooth are coated with cement, which, as its name indicates, serves in many teeth to bind together the other two tissues, as shown in the Ungulates, where the cement in some forms in early stages a complete investment of the crown, and when subjected to wear, occupies the intervals