1. An apparatus is described for measuring the forces exerted on the ground by mammals in three axes at right angles.

2. Analysis of these force records and synchronous photographs of the limb positions shows a constant pattern of activity in the protractor and retractor muscles of both limbs.

3. This pattern of activity is basically the same as that previously demonstrated in the toad and newt and shown to be mechanically in most respects the most efficient possible.

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