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From this video it is evident, that octopus can make tentacles push:

https://youtu.be/zaE-LwDowcU

How is it possible, if it is said, that muscles can only contract?

What types of muscles can distract?

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Kier and Smith wrote a paper on how tongues tentacles and trunks worked. It explains in detail exactly how their legs (and our tongues) elongate, shorten and move about without any bones for support. It's called muscular-hydrostat.

Movement of the limb actually depends on which muscle is being contracted. If it's contracting the muscles longitudinally it will make the limb short and wide, while if it contracts laterally it will cause the limb to extend and be short and thin.

If you watch the video carefully you can actually see the changes in thickness of the limbs as the lateral muscles release and the longitudinal muscles contract so the octopus can move its leg forward.

If you want to see it work in person, go into the bathroom and move your tongue around and watch in the mirror. It uses the same mechanics to move your food around your mouth, lick your teeth, help you get that bit of food that is stuck up against your gum, and who can forget rolling the tongue into a cylinder or making tongue clovers.

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  • $\begingroup$ @SolarLunix I believe Chris suggested you edit your existing answer to include the source, rather than add it as a comment. Might also be helpful if you could add more details to your answer. If I'm reading this right, figure 5 suggests that the muscles around the tentacle contract, squeezing the tentacle into a smaller diameter. Since volume must be constant, the tentacle gets longer. Once the tentacle grabs something, the longitudinal muscles contract and pull the octopus forward, allowing it to walk. $\endgroup$
    – user137
    Jun 1 '15 at 18:24
  • $\begingroup$ Sorry I'm quite new to this site @user137, and as for what you read, that was my understanding as well. $\endgroup$
    – SolarLunix
    Jun 1 '15 at 18:42
  • $\begingroup$ @SolarLunix That's fine, just make the edits and you'll be ok. $\endgroup$
    – user137
    Jun 1 '15 at 20:19
  • $\begingroup$ Shame for me: forgot about myself tongue :))) $\endgroup$
    – Dims
    Jun 2 '15 at 10:58
  • $\begingroup$ @Dims lol we all forget sometimes :D $\endgroup$
    – SolarLunix
    Jun 2 '15 at 16:51

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