Muscles can only pull, not push, so how is it that you can stick out your tongue? In other words, since we have no muscle outside our mouths to pull our tongues out, the fact that muscles are incapable of pushing seems to imply that there is some sort of mechanism at work in producing this movement which doesn’t fit in with our general conception of all other movements (arms, legs, eyes, peristalsis, breathing, et cetera).
i am currently (4/29/08) attending the 18th Annual Neural Control of Movement (NCM) meeting in Naples, Florida, and this tongue question was brought up as a way to remind the attendants that we should be careful not to let dogma affect our thinking too much as such adherence to well-established ideas can prevent us from reaching new ways of understanding and new modes of analysis.
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The simple answer is that the tongue has constant volume, so if you sufficiently contract the muscles in your tongue laterally (from molar to molar), the tongue must increase its volume longitudinally (from throat to lips). Notice also that to really stick your tongue out, you must protrude your mandible significantly.
In any case, it was a perhaps frivolous but highly stimulating and poignant aside in a meeting otherwise devoted to the serious analysis of experimental data, thus kicking things off in a congenial tone.