DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 389 



of being curved in every direction. The feet are extended straight out behind 

 the bird, and appear on the under surface of the tail. The body forms an 

 elongated and very graceful ellipse, admirably adapted for cleaving the air and 

 eluding resistance. 



When the gannet propels itself by the more or less vertical flappings of its 

 wings, the angles which the under surfaces of the wings and body make with the 

 horizon are very considerable — something like 25° or 30°. Of this I convinced 

 myself in a variety of ways.""" When the bird has acquired speed and momentum, 

 and begins to sail, the angle made by the under surfaces of the body and 

 wings is reduced according to circumstances, and in some instances nearly 

 obliterated, the bird gliding along for long distances with its body and wings 

 apparently parallel to the surface of the ocean. 



The wings of the gannet, when fully extended, are curved alternately for- 

 wards and backwards. Thus, the arm and hand are inclined backwards, and 

 the forearm forwards. When the wings are flexed in ordinary flight the move- 

 ment occurs principally at the wrist joint, the arm and forearm bending com- 

 paratively little, and affording a wide basis of support both during the down and 

 up strokes. In forced flight in flexion the wing bends perceptibly at the elbow 

 as well as the wrist, the wing during the up stroke forming a short lever, and 

 being thrown into a fine arch, the convexity of which is directed upwards. The 

 tip of the wing works out and in during the down and up strokes ; and a close 

 examination satisfied me that the bird has the power of forcing the posterior 

 margin of its wings into wave curves while the wings are rising and falling, the 

 air taking no part in the production of the waved movements. 



The down stroke is delivered with perceptibly greater rapidity and energy 

 than the up stroke. Of this there can be no doubt whatever. This allows 

 the air, set in motion by the wing during its descent, time to re-act on the 

 under surface of the pinion so as to contribute to its elevation. This result is 

 facilitated by the wing striking very decidedly downwards and forwards. 



When the gannet alights at its nest it delivers a few very energetic strokes 

 at right angles to the direction of its flight, and thus slows itself. 



When the gannet plunges into the sea from a height it tilts its body until it 

 assumes a more or less perpendicular position, and descends with such impetuosity 

 as to displace the water in an upward direction, until it attains an altitude of 

 from 10 to 15 feet. It flies beneath the water with remarkable rapidity, and 

 emerges without difficulty, the momentum acquired during the descent assisting 

 it through and out of the water. In fact the gannet, when it stoops to pick up 

 a fish, simply describes a continuous downward curve, part of the curve being 



* In the dragon-liy the anterior pair of wings make a smaller angle with the horizon than the pos- 

 terior pair. The first pair of wings are, consequently, more actively engaged as propellors — the second 

 pair as elevators. 



