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voice organ of birds
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voice organ of birds - Voice Organ of birds
voice organ of birds - By their voice, too, birds are distinguished from the rest of the animal creation. Though there may be legends of singing serpents and of talking monkeys, a harsh scream or a growl is the only manifestation of the emotions through the voice which exists until we arrive at man. Among birds, the possession of a melodious voice is limited to that group which we term the Passeres. Other birds can scream or utter a dull note, while many are mute. So flexible is the voice organ of these creatures that they are the only animals that can imitate human speech. Here, however, it is not only the Passeres which can imitate the essential attribute of man. The Parrots, of course, are always supposed to be the birds which can talk, but this is far from being the truth. The hoarse utterances of most Parrots are left far behind in clearness of sound and correctness of imitation by the little Indian Mynah, which may be usually seen at the Zoological Gardens, and heard to speak. But the Parrot cannot sing. These are the only two groups of birds which have so elaborate and flexible an organ of voice. From this it might be inferred that some peculiarities of mechanism would distinguish the organ in question of these birds, and that is what we actually find to be the case. But, oddly enough, it is not only those birds which have a beautiful voice whose voice organs are so elaborate in structure. The harsh croak of the Baven issues from a syrinx which is as delicately fashioned as that which allows of the exquisitely varied tones of the Nightingale. The word ' syrinx ' has been mentioned; that is the technical term for the voice organ of the bird, which is formed from a part of the windpipe, as in man and the mammalia, but from a different part of that tube. In man and in mammals the voice organ is placed in the throat just a little way down, at the prominence often spoken of as 'Adam's apple.' This is a wider part of the tube, with larger rings of cartilage, which contains a pair of tightly stretched membranes that can be made to vibrate and cause a sound. In the bird, the voice organ is situated farther down, at the very point where the trachea forks into the two bronchi, one for each lung. Here are figures which illustrate the voice organ of a singing-bird (figs. 1, 2, 3). At this forking of the trachea the rings of the tube, which are of gristle or cartilage, become somewhat different in form. In the middle is a piece, which is often converted into bone, like the 'three-way' piece used to fix together the stick and the hoop of cane of a butterfly-net. To the upper side of this, and therefore within the tube, and directed upwards, is a little crescent-shaped piece of membrane (h, fig. 3); this can be set vibrating by the stream of air passing up and down the windpipe. At the sides of the syrinx there are shown in the figure (fig. 2) three pairs of muscles; these when they contract shorten the syrinx, and of course produce alterations in the note, just as the shortening of the tube in a cornet alters the sound. In many passerine birds, and in most other birds, there is only one pair of these muscles; but the Parrots agree with the passerines in having several pairs of muscles, and therefore a more easily alterable syrinx. In a good many birds there are no muscles at all in this place; for example, in the Storks, which have not by any means a flexible voice. The syrinx, in fact, is one of those organs which show a great deal of difference in different kinds of birds. But it is never entirely absent, though rather rudimentary in the Ostrich. The Australian Emu has a curious way of producing its sounds which is not found in any other bird. The cock and hen Emus can only be recognised by their voice, which is duller in the hen and sharper in the cock. When the bird is uttering its note, it seems almost to come from somewhere else, and not from the throat of the bird; the bird is something of a ventriloquist. The sound, which is a low bellow, is produced by a bag of skin opening into the windpipe some way up the neck; a current of air passing down the tube is believed to set the air in this bag in vibration, just as the air in a key may be caused to vibrate by blowing over its edge. Generally speaking, the windpipes of birds are straight tubes running to the lungs by the shortest route; but in the Cranes, and in a few other birds, the pipe is coiled upon itself once or twice, and the coils are even hidden in an excavation of the breast-bone. The increased length of tube gives a louder and more resonant note, such as we know characterises the Crane.
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