512 MUSCLE-NERVE PHYSIOLOGY 



cricoid, not only by ligaments, but also by joints with synovial membranes; 

 the lower cornua of the thyroid clasping the cricoid between them, yet not 

 so tightly but that the thyroid can revolve, within a certain range, around an 

 axis passing transversely through the two joints. The vocal cords are attached 

 behind to the front portion of the base of the arytenoid cartilages, and in 

 front to the re-entering angle at the back part of the thyroid; it is evident, 

 therefore, that all movements of either of these cartilages must produce an 

 effect on them of some kind or other. Inasmuch, too, as the arytenoid carti- 

 lages rest on the top of the back portion of the cricoid cartilage, and are 

 connected with it by capsular and other ligaments, all movements of the 

 cricoid cartilage must move the arytenoid cartilages, and also produce an 

 effect on the vocal cords. 



a b 



FIG. 344. The Cartilages and Ligaments of the Larynx, Viewed from the Front, a, 

 Epiglottis; ft, hyoid bone; c, cartilage tritica; d, thyro-hyoid membrane; e, superior cornu of 

 thyroid cartilage; /, thyroid notch; g, pomum Adami; h, crico-thyroid membrane; i, inferior 

 cornu of thyroid cartilage;/, cricoid cartilage. (Cunningham.) 



Intrinsic Muscles. The intrinsic muscles of the larynx are so connected 

 with the laryngeal cartilages that by their contraction alterations in the condi- 

 tion of the vocal cords and glottis are produced. They are usually divided 

 into four classes according to their action, viz., into abductors, adductors, 

 sphincters and tensors. The abductors, the crico-arytenoidei, widen the 

 glottis by separating the cords; the adductors, consisting of the thyro-ary- 

 epiglottici, the arytenoideus posticus seu transversus, the thyro-arytenoidei 

 externi, the crico-arytenoidei laterals, and the thyro-arytenoidei interni, approxi- 

 mate the vocal cords, diminish the rima glottidis, and act generally as sphinc- 

 ters and supporters of the glottis. Finally, the tensors of the cords put the 

 cords on the stretch, with or without elongating them; the tensors are the 

 crico-thyroidei and the thyro-arytenoidei interni. 



The attachments and the action of the muscles will be readily understood 

 from the following table. All the muscles are in pairs except the arytenoideus 

 posticus. 



