The Voice. 375 



vocal cords by being stretched and relaxed produce the 

 pitch of the note emitted; the pitch of the note produced 

 thus depending on the tension of the cords. 



The nerve supply of the larynx is peculiar, and of con- 

 siderable practical interest. Sensation to the mucous 

 membrane, and portion of the epiglottis and glottis, is sup- 

 plied by the superior laryngeal division of the tenth nerve. 

 Motor power is supplied to all the muscles of the larynx, 

 excepting the crico-thyroid, by the inferior laryngeal or 

 recurrent nerve, which is given off from the pneumogastric 

 in the chest : that on the right side winding around the 

 axillary artery and passing up the neck supplies the right 

 larynx, whilst on the left side it passes around the aorta and 

 returns up the neck, in its passage being exposed to aortic 

 pressure and any pressure arising from diseased bronchial 

 lymphatic glands, through the substance of which it passes ; 

 it thus reaches the left side of the larynx and supplies it with 

 motor power. It is this branch of nerve which supplies the 

 muscles implicated in 'roaring,' especially, of course, the 

 inspiratory muscle of the larynx — the crico-arytenoideus 

 posticus. 



The crico-thyroid muscle in the horse is supplied with 

 motor power by the first cervical nerve ; this, according to 

 the experiments of Moeller, is beyond all doubt.* We 

 know that in the most acute case of laryngeal paralysis this 

 muscle is quite sound. Chauveau and others have shown 

 that the spinal accessory supplies the superior laryngeal 

 division of the tenth nerve with motor fibres. 



Swallowing may be excited by touching the vocal cords, 

 but especially the anterior extremity of the arytenoid carti- 

 lages ; the adductor muscles then close and depress the 

 glottis, and the free mucous membrane of the ary-epi- 

 glottic folds, together with the epiglottis, close the entrance 

 into the larynx. The presence of the arytenoid cartilage is 

 not essential to swallowing, or, rather, its presence is not 

 necessary to prevent food passing into the trachea. 



Neighing in the horse is produced by an expiration, 

 * Fleming's ' Roaring.' 



