556 OF THE VOICE AND SPEECH. 



the Vocal ligaments, are effected by the contraction of the Tkyro-ary- 

 tenoidei of the two sides (v &/), whose attachments are the same as 

 those of the Vocal ligaments themselves ; and this is aided by the TJiyro- 

 liyoidei, which will tend to draw up the front of the Thyroid cartilage, 

 acting from a fixed point above. 



976. The muscles which govern the aperture of the glottis, those 

 namely, which separate and bring together the arytenoid cartilages, 

 and thus widen or contract the space between the posterior extremities 

 of the vocal ligaments, have important functions in connexion with 

 the Respiratory actions in general ; standing as guards, so to speak, at 

 the entrance of the lungs. We can entirely close the glottis, through 

 their means, by an effort of the Will, either during inspiration or expi- 

 ration ; and it is a spasmodic movement of this sort, which is concerned 

 in the acts of Coughing and Sneezing, the purpose of which is to expel, 

 by a sudden and powerful blast of air, any irritating substances, 

 whether solid, liquid, or gaseous, which have found their way into the 

 air-passages. These muscles appear to be under the sole direction of 

 the inferior or recurrent laryngeal nerve ; which seems to possess ex- 

 clusively motor endowments. When this nerve is divided, on each side, 

 or when the par vagum is divided above its origin, the muscles of the 

 larynx (with the exception of the crico-thyroid) are paralysed ; and the 

 aperture of the glottis may remain open, or may be entirely closed, ac- 

 cording to the manner in which its lips are affected by the currents of 

 air in ingress or egress. It is found that, under such circumstances, 

 tranquil respiration may be carried on ; but that any violent ingress or 

 egress of air will tend to drive the lips of the glottis (these being in a 

 state of complete relaxation) into apposition with each other, so as com- 

 pletely to close the aperture. The character of the superior laryngeal 

 nerve appears to be almost exclusively afferent ; no muscle, except the 

 crico-thyroid, being thrown into contraction when it is irritated ; whilst, 

 on the other hand, if it be divided, neither the act of coughing, nor any 

 reflex respiratory movement whatever, can be excited, by irritating the 

 lining membrane of the larynx. 



977. During the ordinary acts of inspiration and expiration, the 

 Chordae vocales appear to be widely separated from each other, and to 

 be in a state of the freest possible relaxation. In order to produce a 

 vocal sound, they must be made to approach one another, and their 

 inner faces must be brought into parallelism ; both of which ends are 

 accomplished by the rotation of the Arytenoid cartilages : whilst, at the 

 same time, they must be put into a certain degree of tension, by the 

 depression of the Thyroid cartilage. Both of these movements take 

 place consentaneously, and are mutually adapted to each other ; the 

 vocal ligaments being approximated, and the rima glottidis consequently 

 narrowed, at the same time that their tension is increased. There is a 

 certain aperture, which is favourable to the production of each tone, 

 although the pitch itself is governed by the tension of the Vocal Cords ; 

 and it is, perhaps, to a want of consent between the two, that the pecu- 

 liarly discordant nature of some voices, which appear incapable of pro- 

 ducing a distinct musical tone, is due. 



978. It has been fully proved, by the researches of Willis, Miiller, 



