The Muscular Machinery of Tentacles, Trunks and Tongues

Abstract

A n arm without bones could not bend. A person who tried to bend such an arm would instead end up with a short, fat bulge of biceps. This might score big points at a Mr. Universe contest, but would be fairly useless otherwise. In order to move effectively, muscles which shorten but cannot lengthen on their own accord need bones to work against. Not all animals have bones, however. In insects and other arthropods, for example, muscles instead pull against an external skeleton. And in other invertebrates, including many worm-like animals and polyps such as the sea anemone, muscles work against cavities filled with incompressible fluids. But what of squids, octopi, chambered nautiluses and other cephalopods, which have neither hardened skeletons nor hydrostatic cavities? to everything we're taught, these animals shouldn't be able to function,' says biologist William M. Kier at the University of North Carolina in Chapel Hill. Kier and Kathleen K. Smith, an anatomist at Duke University in Durham, N.C., have solved this muscular mystery by working out the biomechanical principle behind cephalopod movement. Moreover, they've found that the same biomechanics can explain how elephant trunks and human and lizard tongues none of which possess skeletons or hydrostatic cavities are able to move so deftly According to Kier, scientists had remarked on the similarities between the musculature of elephant trunks, tongues and cephalopods in the last century But until now, no one had attempted to explain how all these muscles work, he says. It was just waiting for us.