ANATOMY OF THE VOCAL ORGANS. 551 



backward. They consist of two pairs. The superior, called the false vocal chords, are 

 not concerned in the production of the voice. They are less prominent than the inferior 

 chords, although they have nearly the same direction. They are covered by an excessively 

 thin mucous membrane, which is closely adherent to the subjacent tissue. The chords 

 themselves are composed of fibres of the white inelastic variety, mixed with a few 

 elastic fibres. 



The true vocal chords are situated just below the superior chords. Their anterior 

 attachments are near together, at the middle of the thyroid cartilage, and are immovable. 

 Posteriorly they are attached to the movable arytenoid cartilages ; and, by the action of 

 certain muscles, their tension may be modified, and the chink of the glottis may be opened 

 or closed. These ligaments are much larger than the false vocal chords, and they con- 

 tain a very great number of elastic fibres. Like the superior ligaments, they are covered 

 with an excessively thin and closely adherent mucous membrane. The mucous mem- 

 brane over the borders of the chords is covered with pavement-epithelium without 

 cilia. There are no mucous glands in the membrane covering either the superior or 

 the inferior chords. 



It has been conclusively shown that the inferior vocal chords alone are concerned 

 in the production of the voice. Longet, who has made numerous experiments upon 

 phonation, has demonstrated, by operations upon dogs, that the epiglottis, the superior 

 vocal chords, and the ventricles of the larynx, may be injured, without producing any 

 serious alteration in the voice, but that phonation becomes impossible after serious 

 lesion of the inferior chords. This being the fact, as far as the mere production of the 

 voice in the larynx is concerned, we have only to study the mechanism of the action of 

 the inferior ligaments and the muscles by which their tension and relations are modified. 



Muscles of the Larynx. Anatomists usually divide the muscles of the larynx into 

 extrinsic and intrinsic. The extrinsic muscles are attached to the outer surface of the 

 larynx and to adjacent organs, such as the hyoid bone and the sternum. They are con- 

 cerned chiefly in the movements of elevation and depression of the larynx. The intrinsic 

 muscles are attached to the different parts of the larynx itself, and, by their action upon 

 the articulating cartilages, are capable of modifying the condition of the vocal chords. 

 The number of the intrinsic muscles is nine, consisting of four pairs and a single muscle. 

 In studying the situation and attachments of these muscles, it will be useful at the same 

 time to note their mode of action. 



Bearing in mind the relations and attachments of the vocal chords, we can understand 

 precisely how they can be rendered tense or loose by muscular action. Their fixed point 

 is in front, where their extremities, attached to the thyroid cartilage, are nearly or quite 

 in contact with each other. The arytenoid cartilages, to which they are attached poste- 

 riorly, present a movable articulation with the cricoid cartilage ; and the cricoid, which is 

 narrow in front, and is wide behind, where the arytenoid cartilages are attached, presents a 

 movable articulation with the thyroid cartilage. It is evident, therefore, that muscles act- 

 ing upon the cricoid cartilage can cause it to swing upon its two points of articulation with 

 the inferior cornuaof the thyroid, raising the anterior portion and approximating it to the 

 lower edge of the thyroid ; and, as a consequence, the posterior portion, which carries 

 the arytenoid cartilages and the posterior attachments of the vocal chords, is depressed. 

 This action would, of course, increase the distance between the arytenoid cartilages and 

 the anterior portion of the thyroid, elongate the vocal chords, and subject them to a cer- 

 tain degree of tension. Experiments have shown that such an effect is produced by the 

 contraction of the crico-thyroid muscles. 



The articulations of the different parts of the larynx are such that the arytenoid car- 

 tilages may be approximated to each other posteriorly, though perhaps only to a slight 

 extent, thus diminishing the interval between the posterior attachments of the vocal 

 chords. This action can be effected by contraction of the single muscle of the larynx 

 (the arytenoid) and also by the lateral crico-arytenoid muscles. The thyro-arytenoid mus- 



