STRUCTURE OF ORGANS OF VOICE. small, between the rings, and thus rendering the tube very flexible. This tube greatly varies in form, length, and diameter, and these modifications produce corresponding effects on the character of the voice. Shrill, clear notes, as in singing birds, issue from short tubes; and the various inflexions of these notes are greatly dependent on the slenderness of the rings, and the enlarged spaces between them; whence arises a freedom of motion and a consequent diversity of sound. The tube is, in such cases, governed by a single pair of muscles, which not only give it support, but adapt it to the varied motions of the neck, and influence its length. The longer and wider the tube, and the more it is formed of broad rings, closely approximating, the more monotonous and trumpet-like is the voice. In singing birds it is straight and short; but in the tribe of waders and swimmers it offers every variety of form and convolution. In the velvet duck there is a remarkable hollow bony enlargement, situated two-thirds down the tube, made up of rings firmly ossified together. A similar formation appears also in the goosander, and in the red-crested duck. Among other birds the tube has two remarkable enlargements, with corresponding contractions. STRUCTURE OF ORGANS OF VOICE. But to these varieties of form this organ is not limited; it assumes also folds, more or less intricate. 2 3 Tracheal Tube of the Goosander and of the Red-crested Duck. Section of a part of the Tube of the Velvet Duck, showing the bony enlargement. STRUCTURE OF ORGANS OF VOICE. small, between the rings, and thus rendering the tube very flexible. This tube greatly varies in form, length, and diameter, and these modifications produce corresponding effects on the character of the voice. Shrill, clear notes, as in singing birds, issue from short tubes; and the various inflexions of these notes are greatly dependent on the slenderness of the rings, and the enlarged spaces between them; whence arises a freedom of motion and a consequent diversity of sound. The tube is, in such cases, governed by a single pair of muscles, which not only give it support, but adapt it to the varied motions of the neck, and influence its length. The longer and wider the tube, and the more it is formed of broad rings, closely approximating, the more monotonous and trumpet-like is the voice. In singing birds it is straight and short; but in the tribe of waders and swimmers it offers every variety of form and convolution. In the velvet duck there is a remarkable hollow bony enlargement, situated two-thirds down the tube, made up of rings firmly ossified together. A similar formation appears also in the goosander, and in the red-crested duck. Among other birds the tube has two remarkable enlargements, with corresponding contractions. STRUCTURE OF ORGANS OF VOICE. But to these varieties of form this organ is not limited; it assumes also folds, more or less intricate. 2 3 Tracheal Tube of the Goosander and of the Red-crested Duck. Section of a part of the Tube of the Velvet Duck, showing the bony enlargement. STRUCTURE OF ORGANS OF VOICE. constancy of these convolutions is frequently of great service. They aid him in ascertaining the difference between species nearly alike in outward character; as, for instance, the three species of European swans, which are, indeed, truly distinct. In some birds this tube assumes, as has been already intimated, most singular convolutions, of which that of the wild swan may be given as an example. In this case, the trachea is lodged in a cavity of the keel of the breast-bone, which is opened in the engraving, on page 11, so as to exhibit its convoluted course. It will easily be conceived that the folds of this tube, by which its length is materially increased, would modify the tones of the voice. We find, therefore, such birds uttering deep, grave, monotonous sounds, with more or less of a trumpet-like clang or reverberation. Though the voice is much influenced by the figure, diameter, and firmness of the tube, this is not the part in which it is produced. The true organ of voice-the organ acting on the air as it passes, so as to give it those rapid vibrations, moulded, so to speak, into notes, high or low in the scale, by the tube of the trachea, is the inferior larynx. This is situated at the end of the tube, and is variously constituted in different birds. Every species, indeed, has its own peculiarities. Some |