Page:Popular Science Monthly Volume 13.djvu/739

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TO most people it may appear not only easy enough to distinguish, but even a matter of some difficulty not to be able to identify, a bird from a reptile or from any other animal whatsoever. No one would hesitate for a moment to assign to the bird tribe, on seeing them even for the first time, forms differing from each other so much as the "wingless" apteryx of New Zealand and the strong-pinioned albatross; the marvelously tinted humming-bird and the raw-necked vulture; or the fleet ostrich and the stolid hornbill; for in each individual the eye at once perceives one character at least common to the whole assemblage which is wanting in all other groups. Yet the question to be discussed in this paper of bird or not-bird, and in particular of bird or reptile, is, as we shall see below, one not without serious difficulty.

In order to a more easy comprehension of the question, let us shortly, and with as few technicalities of expression as possible, pass in review the chief characters of the groups we have placed in apposition.

Birds may be characterized generally as feathered bipeds, whose mouth is modified into a longer or shorter beak incased in a horny sheath, sometimes serrated along the margin, but never presenting true teeth; whose fore-limbs assume the form of wings more or less developed, and having the hind-limbs supported on, at most, four toes, the innermost, however, in many birds being so imperfectly developed as not to reach the ground.

Every one who has handled a living bird knows that it is warm-blooded; and whoever, while not neglecting the "main chance," when dining on partridge or fowl, has nevertheless not been too absorbed to mark the prominent points that distinguished the skeletal remains of his feast from those of a hare, for instance, is aware that along the centre of the breastbone there runs a high crest for the attachment of the wing-muscles; that the collar-bones unite to form the bone of destiny with which he has been familiar from his youth as the "merry-thought;" that the haunch-bone, which incloses the bowels and gives attachment to the hind-limbs, differs from a higher quadruped's in being composed, not of two bones (each of which is in reality made up of three bones ossified together), one on each side articulating with yet separate from the spine, and touching each other in the median line beneath, but of these elements and several vertebræ in addition, consolidated into one, having the margins free and separated by a considerable space from each other below; and that instead of a tail, commonly so called, the rear of the spinal column is brought up by what is