How do broad belly scales help snakes crawl?

Broad belly scales, also known as ventral scales, are essential for a specific type of movement in snakes called rectilinear locomotion. In this method, the snake moves in a straight line rather than using lateral curves.12

These scales are elongated crosswise and overlap like roof shingles, with the free edges pointing toward the tail. The movement process works as follows:1

• Lifting: Muscles attached to the ribs lift a scale upward and forward.1
• Anchoring: When the scale is pulled rearward, its edge catches or anchors against the surface.1
• Pushing: Because the scale is anchored, the contraction of the muscles pulls the snake's body forward.1

This sequence is repeated by segments along the body as contraction waves move from head to tail, allowing heavy-bodied snakes, such as boas and some vipers, to inch forward slowly.12