202 ANATOMY OF THE HEAD. 



larynx is the most sensitive of any throughout the body. 

 A grain of salt, or even a drop of water, getting upon it, 

 causes the most sudden and violent spasmodic coughing. 

 The reason for its being made thus sensitive is that it may 

 serve as a guard to the lungs. It is placed on the top of 

 the windpipe ; therefore no foreign body can enter with- 

 out our being immediately informed of the danger. This 

 membrane is thrown into folds, thus forming sacs, spoken 

 of as the ventricles of the larynx ; and it also covers liga- 

 ments, extended across the cavity, for the purposes of voice, 

 and named the cordse vocales. The arteries of the larynx 

 are derived from the carotids, and the veins empty them- 

 selves into the jugulars. Their nerves are furnished by the 

 recurrents and the superior laryngeal, both of which are 

 derived from the par vagum, or eighth pair. 



Uses of the Larynx. — The variations of sound emitted 

 by the voice of quadrupeds appear to be governed principally 

 in the number and form of the laryngeal sacs. There 

 are usually three of these ; one of them is seen under the 

 vault formed by the anterior boundary of the thyroid carti- 

 lage, having its aperture near the root of the epiglottis. 

 The other two are oblong sinuses contained between the 

 lateral parietes of the glottis and the thyroid cartilage ; and 

 are covered in a great measure by the arytenoidei muscles. 

 In the horse these lateral sacs are very long and wide, and 

 are not unlike the usual ventricles of the glottis. The aper- 

 ture of the outer cavity is very large in the horse ; in the 

 ass the opening into each of the three sacs is a small hole, 

 and the anterior sac forms a bag-like cavity. In the mule 

 these organs differ, but their anatomical formation is in 

 general blended between the horse and ass. Neighing ap- 

 pears produced by expirations, as are most of the vocal 

 tones from the horse. The vibrations produced by the 

 resonance of different sized cavities, assisted by the tremors 

 of the cartilages of the nostrils, produce the compound 

 sounds which are emitted. Knuckering, as it is termed, is 

 only a lesser neigh, with shorter, deeper, and less forcible 

 tones, expressive of affection and joy. The horse has one 

 acute sound, produced by the act of inspiration, which 

 usually expresses either play or lust ; but in most other 



