In the third type of lever the fulcrum is at one end, the weight at the other, and the force is placed between them (Fig. 13). The advantage of this arrangement is that a small force causes the extreme point of a long arm to move over a great space.
The mechanism of the muscles acting on the bones illustrates this form of lever. The elbow or joint is the fulcrum, the muscle the moving power, and the weight raised the resistance. The muscles of large migrating birds, for example, must be very powerful in order to sustain the weight of their bodies while they travel for days.