1. Simple methods are described for applying known bending and twisting moments to pigeon bones. The ultimate bending and torsional strengths of the humerus and radio-ulna are determined.

2. Lift distributions are calculated from a strip diagram on the assumption that local lift coefficient is constant across the span. The position of the centre of lift is calculated for (a) gliding, in which the relative air speed is entirely due to the forward motion of the bird; and (b) hovering, in which it is entirely due to rotation of the wing about the shoulder joint.

3. Estimates of the ultimate load factor of the humerus in bending and twisting yielded 8.8 and 9.0 respectively in gliding, and 5.7 and 5.6 in hovering. Corresponding figures for the radio-ulna were 6.9 and 9.1 in gliding, and 4.0 and 5.1 in hovering.

4. The pectoralis insertion is strong enough to apply 4.2g in gliding and 2.9g in hovering, so the muscles would be forcibly extended before any danger could arise of the bones being broken by excessive lift.

5. A lift coefficient of at least 3.4 is achieved during the downstroke of hovering.

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