1. The coefficient of sliding friction between the ventral or lateral surface of a grass-snake varies from 0.2 to 0.6 according to the nature of the surface over which the animal is moving.
2. The distribution and magnitude of the external forces acting against a moving snake has been determined for (i) an animal moving through a close-fitting zigzag channel, and (ii) an animal gliding past one or more rigid pegs. The pattern of muscular effort required for these two types of motion is described. Forward movement is due to the operation of the vertebral column as a series of levers.
3. For a freely moving snake the propulsive force is of the order of one-third of its total body weight; when motion is artificially restrained a grass-snake can sustain a pull of four or five times its own weight.
4. The circumstances under which a snake can exhibit typical terrestrial locomotion as opposed to the movements exhibited in water are fundamentally similar to those of a quadruped such as a toad.