File:The Dental cosmos (1890) (14776863904).jpg

Identifier: dentalcosmos3218whit (find matches)
Title: The Dental cosmos
Year: 1890 (1890s)
Authors: White, J. D McQuillen, J. H. (John Hugh), 1826-1879 Ziegler, George Jacob, 1821-1895 White, James William, 1826-1891 Kirk, Edward C. (Edward Cameron), 1856-1933 Anthony, L. Pierce (Lovick Pierce), b. 1877
Subjects: Dentistry Dentistry
Publisher: Philadelphia, S. S. White Dental Manufacturing Co
Contributing Library: Yale University, Cushing/Whitney Medical Library
Digitizing Sponsor: The College of Physicians of Philadelphia and the National Endowment for the Humanities

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times perfect hexagons, are usually more or lessmodified in form by the obliteration of one or more angles, thus giv-ing rise to the great variety of appearances observed in different speci-mens of ivory. In Fig. 16 I have given a pattern very similar to that seen in Fig.15, under a magnifying power of two hundred and fifty diameters.Here the opaque figures are elongated and their sides so blendedtogether that their hexagonal nature is in most cases not apparent.The two sets of bands, a b, and a b\ are, however, distinctly visible. 426 THE DENTAL COSMOS. The second series of bands or spirals may be entirely wanting, asin the case illustrated in Fig. 14. This is due to the blending togetherof the opaque spots in one set of diagonals, by which the opposite setis naturally destroyed. The object of this arrangement, it may be assumed, is to give greaterstrength and solidity to the ivory, inasmuch as a fracture of thetooth following the direction of the tubuli would present a much Fig. 17.
Text Appearing After Image:
Fig. 17.—Cross-section of a tusk, showing lines of fracture. Fractures parallel (or nearly so)with the direction of the dentinal tubules (a) are in the outer two-thirds distinctly notched ;fractures perpendicular to these (b) are smooth. greater breakage surface than if the tubuli were straight. My atten-tion was first called to this fact by the study of a large tusk, whichhad been broken straight across ; the breakage surface exhibited twoseries of curved, parallel troughs and ridges, cutting each other atvarious angles, so that the whole surface was made up of thousandsof minute pyramids about one millimeter in height. I was able toproduce a similar effect by breaking sections of ivory in differentdirections, thereby obtaining the results illustrated and explained inFig. 17. The tertiary curvatures appear on the crest of the secondary, and ANATOMY AND PATHOLOGY OF THE TUSKS OF THE ELEPHANT. 427 are very short and abrupt ; they are not a constant appearance inivory. As to their cau

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