The vertebrae are very numerous. With the exception of the most anterior
(atlas), all bear ribs, which are very freely movable and are the
snake’s main organs of locomotion. Snakes are capable of moving with
great swiftness. The body undulates from side to side--not up and
down--in a wriggling or writhing fashion. The extremely flexible
backbone permits of this, but to guard against dislocation the vertebrae
are connected by extra locking-joints, which only permit a certain
amount of play. It is, however, comparatively easy to break the back of
a snake by a sharp blow with a stick or whip.