The muscle-powered squeeze catapult mechanism in the family Chameleonidae or chameleons (species <i>Chameleo pardalis</i>).

<p>(A) The chameleon tongue consisting of the tongue skeleton (entoglossal process), accelerator and retractor muscles, and nested collagen sheaths. (B) Activation of spiral-shaped muscle fibers in the accelerator muscle leads to radial contraction and elongation of the muscle and stretches the helically wound collagen fibers in the sheaths. (C–D) The accelerator muscle and sheaths slide off the tip of the bone, releasing the stored elastic energy, and forcing the tongue forward. Drawings based on schematic drawings in [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0158277#pone.0158277.ref030" target="_blank">30</a>]. Scale bar indicates a length of up to 200% body length (peak distance of 30 cm in <i>Chameleo calyptratus</i> [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0158277#pone.0158277.ref030" target="_blank">30</a>]).