The mechanics of amphibian locomotion.

1. A new type of apparatus is described for measuring the forces exerted on the ground by tetrapods in three orthologonal axes simultaneously. 2. From results obtained with toads and newts an analysis of the mechanics of normal amphibian walking is carried out and several features of Gray9s (1944) analysis of the mechanics of the tetrapod skeleton are confirmed. 3. The introduction into the stride of periods of instability is shown to be related to an increase of the length of the stride and is an adaptation to faster movement. 4. The pattern of couples exerted on the limbs by the extrinsic muscles is calculated for the toad and newt. This is found to be basically the same as that in the cat and in man is shown to be, in several important respects, the most efficient possible. 5. The internal mechanics of the toad forelimb is discussed. It is basically similar to that of both fore- and hindlimbs of the newt. The operation of this type of limb is compared to that of a ‘crank’ mechanism and differs in important respects from that of the mammals.