David Harris, Age 9, Of Richmond, Va., for his question:
How can a snake walk without legs?
You cannot do this trick, but a snake can do it with no trouble at all. He can travel over the ground without legs, sometimes quite fast. He can also swim: and many snakes spend all their time in the sea. Some of these legless wonders are champion tree climbers.
A snake gliding over the ground is a graceful creature. And scientists have an elegant name for his weaving, winding way. They call it the lateral undulatory motion. Let's learn what these fancy words mean. Then you can use them when you talk about snakes. And., when you know what lateral undulatory motion means, you will also how know snakes walk without legs.
The word lateral means side or sideways. The word undulatory means wavy. As a rule, a snake travels by curving his body from side to side in graceful waves. The movement begins in his long, supple spine. The ribs move, and they in turn move the snake's scaly skin.
One end of each rib is fixed to the supple spine. The rib curves around the snake's body and ends just under the scaly skin on his underside. The scales overlap each other and farm rough cross folds all along the underside of the snake. Each pair of ribs is loosely fixed to a pair of scales. When the spine curves, the ribs and scales form little bumps to grip the earth.
If you walk on smooth ice., you tend to slip because you cannot get a firm foothold. For the same reason, a snake cannot crawl across a sheet of glass. True, he does not need a foothold, because he has no feet. But he does need firm little pegs. The outside of each snaky curve must be able to push against something solid.
The ground outdoors may be strewn with stones or spiked with grasses. There are plenty of firm pegs against which the snake can push his wavy body. When he slithers through sand or loose soil he digs a furrow and pushes himself forward against the sides of his little ditch.
A few snakes can crawl straight forward, somewhat like a caterpillar. The famous sidewinder throws himself forward by bending his supple body into loops. Most snakes crawl with a lateral undulating motion. Muscles bend the spine in a series of wavy curves. The spine moves the ribs and the ribs form rows of little grippers in the scaly skin on the underside of the snake.