Odontography (Volume 1); Or, a Treatise on the Comparative Anatomy of the Teeth Their Physiological Relations, Mode of Development, and Microscopic St Paperback - 1201

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Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: gous condition may be discerned in the slightly augmented diameter of the enamel-fibres at their peripheral, as compared with their central extremities. When the extremities of the human enamel-fibres are examined with a magnifying power of 300 linear dimensions, by reflected light, they are seen to be co-adapted, like the cells of a honey-comb, and like these to be, for the most part, hexagonal. The external surface of the enamel is marked by fine transverse lines or ridges, of which Retzius counted twenty-four in the vertical extent of one tenth of an English inch of the crown of a human incisor; these lines are parallel and wavy, and, like the analogous markings on the surface of shells, indicate the successive formation of the belts of enamel-fibres that encircle the crown of the tooth. These lines may be traced around the whole crown, but are very faint upon its inner or posterior surface. Retzius cites Leeuwenhoek as the discoverer of these superficial transverse lines of the enamel: but the older observer supposed them to be indicative of the intervals between the successive movements in the cutting of the tooth through the gum. The enamel by virtue of its physical qualities of density and durability forms the chief mechanical defence of the tooth, and is consequently limited, in most simple teeth, to the exterior surface of the exposed portion of the dentine, forming the ' crown ' of the tooth. It sometimes forms only a partial investment of the crown, as in the molar teeth of the iguanodon, the canine teeth of the hog and hippopotamus, and the incisors of the Rodentia. In these the enamel is placed only on the front of the tooth, but is continued along a great part of the inserted base, which is never contracted into one, or divided into more fangs; so that th...