Locomotion
Lack of limbs is no impediment to snakes getting around. Snakes have distinctly different modes of locomotion for different terrain, though some species are more specialized.
Adjustments in locomotion must be made because snake scales create different amounts of friction depending upon direction. Friction is greatest going forward, which is why snakes undulate.
Serpentine locomotion is the well-known side-to-side wiggling. It happens via large ventral plates linked to independent muscle groups, not by shifting ribs, as popularly believed. This lateral undulation is used for crossing uneven surfaces.
A different moving of ventral plates affords rectilinear crawling: a slow advance in a straight line; good for sneaky attack approaches.
Concertina locomotion is most often seen in burrowing snakes, but other snakes use it for crawling through a tube or tight space: the head and front of the body is extended, while the back and tail remain curved, providing an anchor to the ground or sides of a burrow. Once fully extended, the front gains purchase, and draws the tail up.
Desert snakes employ sidewinding: the front of the body makes an arc, then the rest of body moves like a spring. Sidewinding leaves parallel tracks in the sand.
