If muscles can only contract, (e.g. both biceps and triceps are needed to lever your forearms up and down) then how can I swell up my tongue and have it protrude from my mouth? Is it pulled forward from my throat? The control ‘sensation’ seems to lie inside the top surface of the organ. It doesn’t seem as simple as making the organ into a smaller cross-section for the same volume, and it seems to respond too quickly to be a hydro-static thing.