OF THE LARYNX, AND ITS ACTIONS. 847 



of the Arytenoid cartilages, and which, by its contraction, draws them to- 

 gether. By the conjoint action, therefore, of the Crico-aryteuoidei laterales 

 and of the Arytenoideus trausversus, the whole of the adjacent faces of the 

 Aryteuoid cartilages will be approximated, and the points to which the vocal 

 ligaments are attached will be depressed. But if the Aryteuoideus be put in 

 action in conjunction with the Crico arytenoidei postici, the tendency of the 

 latter to separate the Arytenoid cartilages being antagonized by the former, 

 its backward action only will be exerted; and thus it may be caused to aid 

 the Crico-thyroidei in rendering tense the vocal ligaments. This action will 

 be further assisted by the Sterno-thyroidei, which tend to depress the Thyroid 

 cartilage by pulling from a fixed point below ; l and the Thijro-hyoidei will 

 be the antagonists of these, when they act from a fixed point above, the Os 

 Hyoides being secured by the opposing contraction of several other muscles. 

 The respective actions of these muscles will be best comprehended by the fol- 

 lowing table : 



Govern the pitch of the Notes. 



* / CRICO-THYROIDEI, 1 f ^press the front of the Thyroid cartilage on the 

 5 < o T > . . . -< (Jncoid, and stretch the vocal ligaments; assisted 



EI ' ( by the Arytenoideus and Crico-arytenoidei postici. 



f f THYRO-ARYTEXOIBEI, l f Elevate the front of the Thyroid cartilage, and 

 = < rp TT )...< draw it towards the Arytenoids. relaxing the 



*? 1 J. H Y RO- LJ. Y OI DEI . i i- 



[ vocal ligaments. 



Govern the aperture of the Glottis. 

 i CRICO-ARYTEXOIDEI POSTICI, Open the Glottis. 



s 

 o 



SB 



H f CRICO-ARYTKNOIDEI LATERALES,") f Press together the inner edges of the Ary- 



< \ ARYTENOIDEUS TRANSVERSUS, / '" \ tenoid cartilages, and close the Glottis. 



693. The muscles which stretch or relax the Vocal cords are entirely 

 concerned in the production of Voice: those which govern the aperture of 

 the Glottis have important functions in connection with the Respiratory ac- 

 tions in general, and stand as guards (so to speak) at the entrance to the 

 lungs. These separate actions are easily made evident. In the ordinary 

 condition of rest, it seems probable that the Arytenoid cartilages are con- 

 siderably separated from each other ; so as to cause a wide opening to inter- 

 vene between, their inner faces and between the vocal ligaments, through 

 which the air freely passes ; and the vocal ligaments are at the same time 

 in a state of complete relaxation. We can close the aperture of the Glottis 

 by an exertion of the will, during either inspiration or expiration ; and its 

 closure by an automatic impulse forms part of the acts of Coughing and 

 Sneezing ( 304), besides giving rise to those more prolonged impediments 

 to the ingress and egress of air, which have been already noticed as resulting 

 from disordered states of the Nervous system. With these actions, the mus- 

 cles which regulate the tension of the vocal ligaments have nothing to do; 

 and we have seen that they are performed by the instrumentality of the 

 Pueumogastric or proper Respiratory nerve ( 301, 302). The appearances 

 which present themselves when the interior of the Larynx is examined 

 during life are, according to Prof. Czermak, that in the almost semiluuar 



1 These are not usually reckoned among the principal muscles concerned in regu- 

 lating the voice; but that they are so, any one may convince himself by placing his 

 finger just above the sternum, whilst he is sounding high notes; a strong feeling of 

 muscular tension is then at once perceived. 



