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PHYSIOLOGY 



cartilage forwards and downwards, thus approximating the vocal cords at their posterior 

 ends and antagonising the action of the posterior crico-arytenoid muscles. 



(4) The arytenoid muscles consist of transverse fibres, some of which decussate, 

 uniting the posterior surface of the two arytenoid cartilages. When they contract 

 they draw the arytenoid cartilages together. 



(5) The thy ro -arytenoid muscles consist of two portions. The outer fibres rise in 

 front from the thyroid cartilage and pass backwards to be inserted into the lateral 

 border and the muscular process of the arytenoid cartilage. Some of the fibres pass 

 obliquely upwards towards the aryteno-epiglottidean folds. These are often spoken 

 of as a separate muscle, the thyro-epiglottidean. By their action they tend to draw 



Fia. 311. Muscles of the larynx. (SAPPEY.) 

 .A, as shown in a view of the larynx from the right side. 



1, hyoid bone ; 2, 3, its cornua ; 4, right ala of thyroid cartilage ; 5, posterior part of 

 the same separated by oblique line from anterior part ; 6, 7, superior and inferior tubercles 

 at ends of oblique line ; 8, upper cornu of thyroid ; 9, thyro-hyoid ligament ; 10, cartilage 

 triticea; 11, lower cornu of thyroid, articulating with the cricoid ; 12, anterior part of 

 oricoid ; 13, crico-thyroid membrane ; 14, crico-thyroid muscle ; 15, posterior crico- 

 arytenoid muscle, partly hidden by thyroid cartilage. 



B, as seen in a view of the larynx from behind. 



1, posterior crico-arytenoid ; 2, arytenoid muscle ; 3, 4, oblique fibres passing around 

 the edge of the arytenoid cartilage to join the thyro-arytenoid, and to form the aryteno- 

 epiglottic, 5. 



the arytenoid cartilages forwards and to relax the vocal cords. The upper fibres may 

 also assist in depressing the epiglottis. The inner fibres are called the muscidus vocalis. 

 They arise from the lower half of the angle of the thyroid cartilage, and passing back- 

 wards in the vocal cords are attached to the vocal processes and to the adjacent parts 

 of the outer surfaces of the arytenoid cartilages. Many fibres do not run the whole 

 distance, but end in an attachment to some part of the vocal cord. Although their 

 action must be to draw the arytenoid cartilages forwards, yet, since they are contained 

 in the vibrating portion of the vocal cords, they cannot by their contraction relax 

 these cords. It is probable that they play a great part in determining the tension of 

 the vocal cords after these have been put on the stretch by the action of the crico -thyroid 

 muscles. They may possibly act as a sort of fine adjustment of the tension, the coarse 

 adjustment being represented by the crico -thyroids. 



