How Can Snakes Crawl Without Feet?

Snakes have a long spine which is formed by many vertebrae that are linked to each other. There is a rib on each side of every vertebrae Because every rib connected with the scale on the belly, each pair of ribs can move forward or backward freely. When the spine muscles contract, the ribs drive the scales to move about. The snake uses its scales like the tread of a tractor to crawl forward.