From the case:
Eustachian tube (illustration)
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Eustachian Tube
Image from Gray's Anatomy 1918. This faithful reproduction of a lithograph plate from Gray's Anatomy, a two-dimensional work of art, is not copyrightable in the U.S. as per Bridgeman Art Library v. Corel Corp.; the same is also true in many other countries, including Germany. Unless stated otherwise, it is from the 20th U.S. edition of Gray's Anatomy of the Human Body, originally published in 1918 and therefore lapsed into the public domain.