ABSTRACT
The propulsion of an undulating grass-snake, Natrix (Tropidonotus) natrix, depends on the ability of the animal to adopt a sinusoidal form and brace the lateral surface of its body against rigid external objects (Gray, 1946). Under such conditions the forces acting normally to the sides of the body provide a propulsive force equal but opposite to the frictional forces tending to restrain the motion of the animal. The present paper represents an attempt to give quantitative expression to these conclusions by observation of the forces acting against the body of a living snake.
If the radius of the peg is r, that of the ‘circle of friction’ is r sin θ, where θ is the angle whose tangent is equal to the coefficient of lateral friction (μ). See Fig. 10, Folder III.
See Folder III.
See Folder I.
See Folder II.
For Figs. 10 –12 see Folder III.
By appropriate muscular activity, the snake can also brace the ventral surface of the body against transverse friction exerted by the ground ; this force is probably small in comparison with the lateral friction exerted by rigid external resistances or the longitudinal ventral friction, and will only be considered to a very limited extent in this paper (see Fig. 10 (iv) Folder III).
For Figs. 6, 7 and 8 see Folder I.
See Folder IV.
See Folder IV.
