Combination of 2 images: <a href="//commons.wikimedia.org/wiki/File:Cardinal_vowel_tongue_position-front.png" title="File:Cardinal vowel tongue position-front.png">front</a> and <a href="//commons.wikimedia.org/wiki/File:Cardinal_vowel_tongue_position-back.png" title="File:Cardinal vowel tongue position-back.png">back</a> vowels
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Jones, Daniel. (1972). An outline of English phonetics (9th ed.). Cambridge: W. Heffer &amp; Sons Ltd.