This study reveals that: 1) the retraction of the hoof or foot relative to the hip at the end of the support phase is less in the horse than in the dog; 2) the change in the sense of the movements of the hind limb segments at the end of the support phase and at the beginning of the swing phase occurs earlier in the horse (55–60% of the cycle of a stride) than in the dog (70%); 3) in neither species is there activity in the retractor muscles of the hind limb at the end of the support phase, so that the push-off is effected by the dynamic effect of the load (gravity) and the elastic resilience of the retractor muscles; 4) in the horse, the cannon passes bevond the vertical and makes it necessary to bring the cranial tibial muscle into action to prevent overextension of the hock joint; in the dog, the metatarsus remains in an approximately vertical position and the superficial digital flexor muscle remains active throughout the support phase; 5) at placing, the moment ofF _I(Fig. 1) about the foot provokes a tensile strain on the plantar aspect of the tibia and a compressive strain on its dorsal aspect: the action of the gastrocnemius muscle centres the line of action of the load on the tibia in this phase; 6) at the end of the support phase, the relatively greater moment of F _Iabout the hoof of the horse makes it necessary to bring the cranial tibial muscle into action to centre the line of action of the load on to the tibia; 7) the tendinous interosseous and superficial digital flexor muscle of the horse store elastic energy at impact and use this energy to stretch the peroneus tertius tendon, the energy ultimately being used to flex the hock at lifting; the superficial digital flexor and the peroneus tertius tendons coordinate the movements of stifle and hock during the swing phases; all the components mentioned save energy: the horse is an animal built for great stamina; 8) in the dog, the analoga of the aforementioned tendons are muscular; consequently the dog is able to dig its digits and claws into the ground for a strong grip and great friction: the digitigrade dog is adapted and for great speed.