How the snake pours its way across the ground

Snakes move in mysterious ways. Sometimes they slither along in the grass as you might expect, if snakes are ever expected.

Sometimes they rise straight up as if levitating. They leap across wide gaps. They even fly, some of them, or at least glide, launching themselves into the air from trees they have climbed. And then there’s the sidewinder, named for its hypnotic motion.

Scientists, like Bruce Jayne, at the University of Cincinnati, have long studied snake locomotion, and almost all the ways snakes move involve bending and twisting the body.

But Jayne and his graduate student, Steven J. Newman, analyzed another kind of locomotion in a recent issue of the Journal of Experimental Biology.

This one involves moving in a straight line, with no bending.

A scientist named Hans Lissmann described it about 70 years ago and developed a hypothesis about what muscles the snakes use to propel themselves, and how those muscles act.

Lissmann, Jayne said, “did some classic work.”

“We had an extremely good idea of all of the movements,” he said. “But what we were really lacking were any direct observations of how the muscles work.”

Newman inserted fine wire electrodes in the snakes’ muscles to record their activity, something like the way sensors record heart activity in an electrocardiogram.

What the scientists found was that Lissmann was mostly right, but not exactly so.

As the snake moves forward, a muscle in its belly skin shortens the skin and stays tensed. Then a muscle running forward from the tip of one rib to the skin tenses to pull the skeleton and body forward over the skin. Another muscle that runs toward the tail from the middle of a rib to the skin pulls the skin forward.

Lissmann did not expect the skin muscle to stay tensed, and he thought the skin muscles did the work of pulling the body forward.

The results might be of use in creating soft, snakelike robots meant to find their way through nooks and crannies without troublesome legs to snag on obstacles.