CH. LV.] 



MUSCLES OF THE LAEYNX 



753 



within a certain range, around an axis passing transversely through the two joints 

 at which the cricoid is clasped. The vocal cords are attached behind to the front 

 portion of the base (vocal process) of the arytenoid cartilages, and in front to the 

 re-entering angle at the back of the thyroid ; it is evident, therefore, that all move- 

 ments ot either of these cartilages must produce an effect on them of some kind or 

 other. Inasmuch, too, as the arytenoid cartilages rest on the top of the back portion 

 ot the cricoid cartilage, and are connected with it by capsular and other ligaments, 

 I movement of the cricoid cartilage must move the arytenoid cartilages, and also 

 produce an effect on the vocal cords. 



F.V.C 



V.C. 



T.C.M. 



f*uu"T The larynx is lined with a mucous membrane continuous 

 with that of the trachea ; this is covered with ciliated epithelium except over the vocal 

 cords and epiglottis, where it is 

 stratified. The vocal cords are 

 thickened bands of elastic tissue in 

 this mucous membrane which run 

 from before back. They are at- 

 tached behind to the vocal processes 

 of the arytenoid cartilages, and in 

 front to the angle where the two 

 wings of the thyroid meet The 

 chink between them is called the 

 rima glottidis (see fig. 554). Two 

 ridges of mucous membrane above 

 and parallel to these are called the 

 false vocal cords: between the true 

 and false vocal cord on each side is 

 a recess called the ventricle. 



Muscles. The muscles of the 

 larynx are divided into intrinsic and 

 extrinsic. The intrinsic are named 

 from their attachments to the various 

 cartilages; the extrinsic are those 

 which connect the larynx to other 

 parts like the hyoid bone. 



The intrinsic muscles of the 

 larynx are as follows: 



1. Crico-thyroid. 



2. Posterior crico-arytenoid. 



3. Lateral crico-arytenoid. 



4. Thyro-arytenoid. 



5. Arytenoid. 



All these muscles except the 

 arytenoid are in pairs. 



Their attachments and actions 

 are as follows : 



1. Crico-thyroid. This is a 

 short, thick triangular muscle, at- 

 tached below to the cricoid cartilage ; 



this attachment extends from the middle line backwards. The fibres pass upwards 

 and outwards, diverging slightly to be attached above to the inferior border of the 

 thyroid cartilage, and to the anterior border of its lower cornu. In the latter portion 

 of the muscle, the fibres are nearly horizontal Some of the superficial fibres are 

 continuous with those of the inferior constrictor of the pharynx. 



The thyroid cartilage being fixed by extrinsic muscles, the contraction of this 

 muscle draws upwards the anterior part of the cricoid cartilage, and depresses the 

 posterior part, and with it the arytenoid cartilages, so that the vocal cords are 

 stretched. Paralysis of these muscles therefore causes an inability to produce high- 

 pitched tones. 



2. Posterior crico-arytenoid. This arises from the broad depression on the 

 corresponding half of the posterior surface of the cricoid cartilage ; its fibres con- 



3 B 



FIG. 554. Vertical section through the larynx, passing 

 from side to side. H, Hyoid bone ; T., thyroid carti- 

 lage ; T.C.M., thyro-cricoid membrane ; C., cricoid 

 cartilage ; Tr., first ring of trachea ; T.A., thyro- 

 arytenoid muscle ; R.G., rima glottidis; V.C., vocal 

 cord ; V., ventricle ; F.V.C., false vocal cord. (After 

 Allen Thomson.) 



