. The bird, its form and function . ^G. 320. Fig. 321. Tail of Barn Swallow, closed (320) and spread (321). body by several movable joints. The real tail of a birdis the small, fleshy protuberance which in our roastchicken we call the popes nose; but in common par-lance the word tail has come to be applied to the largefeathers which sprout from this structure. Thus, althoughnot comparable to the appendages of mammals, the so-called tail of a bird is superficially more like the correspond-mg organ of a whale than the tail-fin of a fish, since it isexpanded horizontally instead of vertically. 4o
. The bird, its form and function . ^G. 320. Fig. 321. Tail of Barn Swallow, closed (320) and spread (321). body by several movable joints. The real tail of a birdis the small, fleshy protuberance which in our roastchicken we call the popes nose; but in common par-lance the word tail has come to be applied to the largefeathers which sprout from this structure. Thus, althoughnot comparable to the appendages of mammals, the so-called tail of a bird is superficially more like the correspond-mg organ of a whale than the tail-fin of a fish, since it isexpanded horizontally instead of vertically. 4o6 The Bird One interesting analogy to the fin of a fish is foundin the tail of the Blue Duck of New Zealand. This birdlives in swift mountain streams and when swimming carriesits long tail entirely submerged. By vigorous sidewiseflicks of these tail-feathers it can turn around, as if on apivot, without being carried down-stream, even whenin the centre of a rapid, swirling Pig. 322.—Murre showing tail. (Compare with Fig. 246.) It is interesting to compare this use of the tail-featherswith the function of the tail in the flightless the Black-footed species, at least, the tail-feathers arestiff and short, but the bones of the tail are unusuallyelongated and the flesh which covers them is flattenedinto a kind of vertical rudder. Strong muscles control Tails 407 this, and by it the extremely quick dives and turns aremade possible. No feather would be stiff or rigid enoughto offer to the water the resistance which these featheredseals require. Exceptions to the rudder use in flying birds are foundin the murres—sea-birds which share the cliffs of our north-ern coast with cormorants and gulls. The tail-feathersof a murre are so short as to be useless for steering pur-poses, so in flight the bird uses its webbed feet instead,stretching them out behind, opening, turning, and twist-ing them in harmony with the wings, with as satisfactoryresults as
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