. The animans and man; an elementary textbook of zoology and human physiology. feathers, the modificationof the fore limbs into wings, and the toothless, beaked mouthare characteristic and distinguishing external feathers, although covering the whole of the surface ofthe body, are not uniformly distributed, but are groupedin tracts called pterylce, separated by bare or downy spacescalled apteria. They are of several kinds, the short softplumules or down-feathers, the large stiffer contour-feathers,whose ends form the outermost covering of the body, thequill-feathers of the wings a
. The animans and man; an elementary textbook of zoology and human physiology. feathers, the modificationof the fore limbs into wings, and the toothless, beaked mouthare characteristic and distinguishing external feathers, although covering the whole of the surface ofthe body, are not uniformly distributed, but are groupedin tracts called pterylce, separated by bare or downy spacescalled apteria. They are of several kinds, the short softplumules or down-feathers, the large stiffer contour-feathers,whose ends form the outermost covering of the body, thequill-feathers of the wings and tail, and the fine bristles orvibrissae about the eyes and nostrils called fore limbs are modified to serve as wings, which arewell developed in almost all birds. However, the strangeKiwi or Apteryx of New Zealand with hair-like feathers is 214 THE VERTEBRATES: BIRDS 215 almost wingless, and the penguins have the wings so reducedas to be incapable of flight, but serving as flippers to aid inswimming underneath the water. The ostriches and cas- •<. FIG. 111. Cardinal grosbeak, or red bird, Cardinalis cardinalis. (One-half natural size; from life.) sowaries also have only rudimentary wings and are not ableto fly. Legs are present and functional in all birds, vary-ing in relative length, shape of feet, etc., to suit the specialperching, running, wading, or swimming habits of thevarious kinds. Living birds are toothless, although certain 2l6 THE ANIMALS AND MAN extinct forms, known through fossils, had large teeth set insockets on both jaws. The place of teeth is taken, as faras may be, by the bill or beak formed of the two jaws, pro-jecting forward and tapering more or less abruptly to a most birds the jaws or mandibles are covered by a hornysheath. In some water and shore forms the mandibularcovering is soft and leathery. The range in size of birds isindicated by comparing a humming-bird with an ostrich.
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