300 OF THE VOICE AND SPEECH. 



deus lateralis, which runs forwards and downwards from the outer corner of 

 the Arytenoid cartilage ; and its action, with that of its fellow, will be to bring 

 the anterior points of the Arytenoid cartilages into the same straight line, at 

 the same time depressing them, and thus to close the Glottis. This muscle is 

 assisted by the Arytenoideus transversus, which connects the posterior faces 

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

 gether. By the conjoint action, therefore, of the Crico-arytenoideus lateralis, 

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

 Arytenoid cartilages will be pressed together; and the points to which the 

 vocal ligaments are attached will be depressed. But if the Arytenoideus 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-thyroideus in rendering tense the vocal ligaments. This action 

 will be further assisted by the Sterno-thyroideus, which tends to depress the 

 Thyroid cartilage, by pulling from a fixed point below ;* and the Thyro-hyoi- 

 deus will be the antagonist of this, when it acts from a fixed point above, the 

 Os Hyoides being secured by the opposing contraction of several other mus- 

 cles. The respective actions of these muscles will be best comprehended by 

 the following table. 



Govern the Pitch of the Notes. 



^ CDenress the front of the Thyroid cartilage on the 



> C CRICO-THYROIDEI | .... 3 Cricoid, and stretch the vocal ligaments; assisted 

 S^STERXO-IHYROIDEI 3 by the Arytenoideus and Crico-arytenoidei postici. 



("Elevate the front of the Thyroid cartilage, and draw 

 I ) THTRO HYi OII)EI }'") il towards lhe Arytenoids, relaxing the vocal liga- 



Govern the Aperture of the Glottis. 

 l> 

 5. CHICO-ARYTENOIDEI POSTICI '. . . . . Open the Glottis. 



C CRICO-ABYTENOIDEI LATEBALES? . . C Press together the inner edges of the Ary- 

 5T ABYTENOIDECS J " " C tenoid cartilages, and close the Glottis. 



F 



404. The muscles which stretch or relax the Vocal ligaments, are entirely 

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

 Glottis have important functions in connection with the Respiratory actions in 

 general, and stand as guards (so to speak) at the entrance to the lungs. Their 

 separate actions are easily made evident. We can close the aperture of the 

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

 it is a kind of spasmodic movement of this sort, which is concerned in the acts 

 of Coughing and Sneezing ( 189), as well as in the more prolonged impedi- 

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

 resulting from disordered states of the Nervous system ( 300). A slight 

 examination of the recent Larynx is sufficient to make it evident that, when 

 once the borders of the Rima Glottidis are brought together by muscular 

 action, the effect of strong aerial pressure on either side, whether produced 

 by an expulsory blast from below, or by a strong inspiratory effort, occasioning 

 a partial vacuum below, and consequently an increased pressure above, will 



* This is not usually reckoned as one of the principal muscles concerned in regulating 

 the voice ; but that it is 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. 



