Make a vowel like the i: in the English word 'see' and look in a mirror; if you tilt your head back slightly you will be able to see that the tongue is held up close to the roof of the mouth. Now make an ae vowel and notice how the distance between the surface of the tongue and the roof of the mouth is now much greater. The difference i: as a relatively close vowel and ae as relatively open vowel. Tongue height can be changed by moving the tongue up or down, or moving the lower jaw up or down. Usually we use some combination of the two sorts of movement, but when drawing side-of-the-head diagrams such as Fig. 1 and Fig. 2 it is usually found simpler to illustrate tongue shapes for vowels as if tongue height was altered by tongue movement alone, without any accompanying jaw movement. So we would illustrate the tongue height difference between i: and ae as in Fig. 3.