Page:The Hog.djvu/119

117 a seemingly complicated but really simple muscular apparatus. In form it is an irregular oblong tube, exceedingly flexible, and capable of adapting itself to all the natural or morbid changes of the respiratory process, and to the production of all the various intonations of sound or voice by which the animal expresses his emotions. It is placed at the top of the windpipe, guards the exit from the lungs, and prevents the passage of food into the respiratory canals.

The Ericoid cartilage constitutes the base and support of this organ, and serves in great measure as a bond of union to the rest.

Placed above and resting upon this are the Arytenoid cartilages, prolongations of which rest upon the Chordæ vocales, and influence their action. The vocal ligaments take an oblique direction across the larynx in the pig instead of a straight one, so that the angle is at a considerable distance from the thyroid cartilage. They have also a curious slanting direction, the anterior angle being depressed and the arytenoid portion elevated. About the middle of the chordæ vocales, and immediately above them, are two sacculi, which are generally supposed to be concerned in the act of grunting. From the anterior parts of the larynx springs the epiglottis, a heart-shaped cartilage placed at the extremity of the opening into the windpipe, with its back opposed to the pharynx; its use is this: food passing from the pharynx in its way to the œsophagus presses down the epiglottis, which, closing the aperture of the larynx, prevents any portion of the food from entering it. As soon as the food has passed, the elasticity of the epiglottis, assisted by that of the membrane at its base, and still more by the power of the hyo-epiglottideus muscle, enables that cartilage to rise up and resume its natural position.

The thyroid cartilage envelops and protects all the rest, and shields the lining membrane of the larynx, which vibrates under the impulse communicated by the passage of the air, and gives the tone or voice.

In the larynx of the hog we find that beautiful adaptation of means to the end. The space between the arytenoid cartilages is less, comparatively speaking, than in the horse or dog, speed not being required in swine. The epiglottis, too, is larger than in the ox, sheep, or horse, and differently constructed; it is more flexible, from the cellular ligamentous substance at the base of it being looser; and from its increased size, and the curved direction of its edges, it not only covers the opening into the windpipe, but in a manner embraces the arytenoid cartilages when pressed down by the passage of food, a formation admirably suited to an animal who is constantly plunging his nose and muzzle into the mud or dirt, and who, by blowing into his food in the peculiar way pigs are apt to do in order to stir up the sediment, would otherwise be constantly getting some irritating and noxious matters into his windpipe. The inferior cornu of the thyroid bone is comparatively more developed in the hog than in other domesticated animals.