Editing Muscular hydrostat (section)

===Elongation and shortening===

[[File:Abralia veranyi tentacles.jpg|thumb|Arms and tentacles of the squid ''[[Abralia veranyi]]'']]
Elongation in hydrostats is caused by the contraction of transverse or helical musculature arrangements. Given the constant volume of muscular hydrostats, these contractions cause an elongation of the longitudinal muscles. Change in length is proportional to the square of the decrease in diameter.<ref name=Kier1985 /> Therefore, contractions of muscles perpendicular to the long axis will cause a decrease in diameter while keeping a constant volume will elongate the organ length-wise. Shortening, on the other hand, can be caused by contraction of the muscles parallel to the long axis resulting in the organ increasing in diameter as well as shortening in length.

The muscles used in elongation and shortening maintain support through the constant volume principle and their antagonistic relationships with each other. These mechanisms are seen often in prey capture of [[shovelnose frog]]s and [[chameleon]]s, as well as in the [[human tongue]] and many other examples. In some frogs, the tongue elongates up to 180% of its resting length.<ref>Nishikawa, K. C.; Kier, W. M.; Smith, K. K. (1999). "[http://jeb.biologists.org/content/202/7/771.short Morphology and mechanics of tongue movement in the African pig-nosed frog ''Hemisus marmoratum'': a muscular hydrostatic model http://jeb.biologists.org/content/202/7/771.short]". ''The Journal of Experimental Biology'' '''202''': 771–780.</ref> Extra-oral tongues show higher length/width ratios than intra-oral tongues, allowing for a greater increase in length (more than 100% of resting length, as compared to intra-oral tongues at only about 50% of resting length increase). Greater elongation lengths trade off with the force produced by the organ; as the length/width ratio is increased elongation increases while force is decreased.<ref name=Kier&Smith1985 /> Squids have been shown to use muscular hydrostat elongation in prey capture and feeding as well.<ref name=Kier1982 />