The Dental cosmos . ff by a greater degree of opacity and usually also by a browncolor, which latter, however, is probably a post-mortem production.(See Fig. 8.) 346 THE DENTAL COSMOS. The body of the dentine or ivory presents appearances characteristicof the tusks of the Proboscidean, of which the elephant is the only nowexisting species. Adjacent to the border-line between the cementand dentine, alternating opaque and semi-transparent curved lines orlayers are seen to arise, and, passing at first nearly parallel with theperiphery of the section, describe curves resembling the spiral ofArchim
The Dental cosmos . ff by a greater degree of opacity and usually also by a browncolor, which latter, however, is probably a post-mortem production.(See Fig. 8.) 346 THE DENTAL COSMOS. The body of the dentine or ivory presents appearances characteristicof the tusks of the Proboscidean, of which the elephant is the only nowexisting species. Adjacent to the border-line between the cementand dentine, alternating opaque and semi-transparent curved lines orlayers are seen to arise, and, passing at first nearly parallel with theperiphery of the section, describe curves resembling the spiral ofArchimedes, making one-half to three-fourths of a revolution towardthe center of the tooth. Of these spirals there are two sets, one passingto the right, the other to the left; crossing each other, they produce,near the border of the cement, elongated diamond- or lozenge-shapedfigures ; farther beneath the border squares or hexagons, and near thecenter of the tooth are other diamond-shaped figures, which, however, Fig. Fig. 9.—Longitudinal section through the center of a full tusk. stand at right angles to those near the border. (See Figs. 6-8.) Ofthis, which may be considered the normal arrangement, there occurso many modifications that I shall not attempt to describe each oneseparately. Oblique sections cut at any angle between 150 and 900show to the naked eye the same appearance as cross-sections, as maybe readily gathered from the study of a billiard-ball cut from the heartof the tusk. Longitudinal sections passing through the heart of the tooth or nearlyso present a series of alternating dark and light zones, about one milli-meter in thickness, and describing a small angle with the axis of thetooth ; that is, they run parallel with the direction occupied by thesurface of the pulp at the time they were formed. These zones suc-ceed each other sometimes with tolerable regularity, at other timesthey run into each other and present frequent ramifications (Fig. 9). ANATOMY AND P
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