654 THE VOICE. [BOOK in. 



Widening of the Glottis. The crico-arytenoideus posticus 

 passing from the posterior surface of the cricoid cartilage to the 

 outer angle of the arytenoid cartilage behind the attachment of 

 the lateral crico-arytenoideus, pulls back this outer angle, and so 

 causing the processus vocalis to move outwards, widens the glottis. 

 The arytenoideus posticus, acting alone, has a similar effect. 



Tightening of the Vocal Cords. The crico-thyroideus pulls 

 the thyroid downwards and forwards, and so increases the distance 

 between that cartilage and the arytenoids when the latter are 

 fixed. Supposing then the arytenoideus and crico-arytenoideus. 

 posticus to fix the arytenoids, the effect of the contraction of the 

 crico-thyroideus would be to tighten the vocal cords. 



Slackening of the Vocal Cords. This is effected by the whole 

 sphincter group just mentioned, but more especially by the thyro- 

 arytenoidei externus and internus ; these acting alone, supposing 

 the arytenoid cartilages to be fixed, would pull the thyroid car- 

 tilage upwards and backwards, and so shorten the distance between 

 the processus vocales and that body. 



Thus almost every movement of the larynx is effected not by 

 one muscle only but by several, or at least by more than one, 

 acting in concert. The movements which give rise to the voice 

 are preeminently combined and coordinate movements. When 

 we remember how a very slight variation in the tension of the 

 vocal cords must give rise to a marked difference in the pitch of 

 the note uttered, and yet what a multitude of fine differences of 

 pitch are at the command of a singer of even moderate ability, it 

 appears exceedingly probable that the various muscular com- 

 binations required to produce the possible variations in pitch are 

 of such a kind that frequently a part only, possibly a few fibres 

 only, of a particular muscle, may be thrown into contraction, while 

 all the rest of the muscle remains quiet. Taking into view 

 moreover the great range of pitch possessed by even common 

 voices, as compared with the possible variations of tension of 

 which the vocal cords in their natural length are capable, it has 

 been suggested that some of the fibres of the thyro-arytenoideus 

 internus, which passing either from the thyroid or from the 

 arytenoid, appear to end in the vocal cords themselves, may, by 

 fixing particular points of the cords, so to speak, 'stop' them ; and 

 by thus artificially shortening the length actually thrown into 

 vibration, produce higher notes than the cords in their natural 

 length are capable of producing. It has been also suggested that 

 the processus vocales may overlap each other, and thereby shorten 

 the length of cord available for vibration. 



These various muscles are supplied by the vagus nerve, or 

 rather by spinal accessory fibres running in the vagus trunk. The 

 superior laryngeal is the afferent nerve supplying- the mucous 

 membrane, but it also contains the motor fibres distributed to the 



