The elegant spiral
horn of the narwhal or sea-unicorn also produces ivory of a superior
quality. It is not to any great extent applied to useful purposes, but
is more frequently preserved in museums and collections as a beautiful
natural curiosity.
The tusks and teeth of the elephant--the latter, for the sake of
distinction, are termed grinders--are formed after the ordinary manner
of the teeth of animals. The organism which converts the earthy
constituents of the blood into cellular tissue and membrane,
contributes in the same way to form the teeth by the successive
deposition of layer upon layer of the soft vascular pulp. The marks of
these depositions, or laminae, are clearly distinguishable in the
longitudinal striae of the section of a tooth. Mr Corse Scott states
that the Indian elephant has only ten or twelve laminae in the tooth,
while that of the great mammoth has twenty-four, besides having a much
more regularly disposed enamel. The tooth is hollow about half-way up,
but a very small tubular cavity is visible throughout its entire
length. This, sometimes called the nerve, is in reality the apex of
successive formations in the process of growth. The grinders are
seldom used in the arts.
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