Snakes do not have feet or legs, but instead propel themselves forward using their ventral scales. Ventral scales are much like tire treads on a car, allowing the snake to grip.
Researchers say that snakes have not always been legless. Research published in the Journal of Vertebrate Paleontology suggests that snakes at one time had legs, but that they evolved without them because they became less useful and grew less over time. Their research is based on snake specimens unearthed that date back to up to 112 million years ago that suggest that snakes had legs. Specimens from 90 million years ago show the regression in legs and the move towards the legless species we recognize today.