THE HEAD AND NECK 1291 



cartilage. Some of the fibres are continuous with those of the 

 external portion of the thyro-axytenoid muscle. 



Nerve-supply. — The inferior or recurrent laryngeal nerve. 



Action. — To draw the aiytenoid cartilages together, so as to 

 approximate the true vocal cords, and even close the rima glottidis. 



The ar\tenoideus transversus muscle, clothed with mucous mem- 

 brane internally, boimds the rima glottidis posteriorly; and its 

 superficial or posterior surface supports the decussating arytenoidei 

 obhqui muscles. 



Compressor Sacculus Laryngis, or Hilton's Muscle. — This is the 

 name given to a thin layer of muscular fibres on the inner side and 

 upper end of the sacculus lar^Tigis. The fibres are related superiorly 

 to those of the arytaeno-epiglottideus, which are contained within 

 the aryteno-epiglottidean fold. 



Summary of the Actions of the Laryngeal Muscles. — The intrinsic 

 muscles of the larynx, by regulating the condition of the rima 

 glottidis, contribute to vocalization, and modify the pitch of notes. 

 In so doing they lengthen, so as to render tense, or shorten, so as 

 to relax, the vocal cords ; and they also bring the cords together, 

 or draw them apart. In other words, the intrinsic muscles bring 

 about tension and parallelism of the true vocal cords, or give rise to 

 the opposite conditions, namely, relaxation and divergence. 



Tension is effected by the crico-thjToid muscles, which swing the 

 anterior part of the cricoid cartilage upwards and backwards 

 towards the thyroid, the result being to increase the distance 

 between the receding angle of the thyroid cartUage and the vocal 

 processes of the arytenoid cartilages. In this manner the true 

 V'ocal cords are stretched, and tension of them is produced. 



Parallelism of the true vocal cords is effected by (i) the lateral 

 crico-arytenoid muscles, and (2) the arytenoid muscle, the latter 

 also producing narrowing of the glottis respiratoria (interarytenoid 

 portion of glottis). The lateral crico-arjrtenoid muscles draw 

 forwards the muscular processes of the arytenoid cartilages, the 

 result of which is to swing inwards the vocal processes, and so 

 produce parallelism. The arytenoid muscle draws the arytenoid 

 cartOages together, and so narrows the glottis respiratoria, con- 

 tributing at the same time to the condition of parallelism. 



Relaxation of the true vocal cords is brought about by the thyro- 

 arytenoid muscles, which draw the arytenoid cartilages, along with 

 the posterior part of the cricoid cartilage, forwards. In this manner 

 the distance between the receding angle of the thyroid cartilage and 

 the arytenoid cartilages is diminished, and so relaxation of the 

 true vocal cords is produced. They are at the same time shortened 

 in virtue of their elastic recoU. The fibres of the thyro- arytenoid 

 muscle, known as the ary-vocalis, act by rendering tense the part 

 of the true vocal cord in front of them, and relaxing the part behind 

 them (Ludwig). 



Divergence of the true vocal cords and opening of the rima glottidis 

 is effected by the posterior crico-arj-tenoid muscles, which draw 

 *^e muscular processes of the arytenoid cartilages backwards and 



