"90 A MANUAL OF ANATOMY 



Nerve-supply. — ^The recurrent laryngeal nerve. 



Action. — (i) Internal Portion. To draw forwards the arytenoid 

 cartilage, and the posterior part of the cricoid cartilage, swinging 

 the latter in an upward and forward direction. The result of this 

 action is to relax the true vocal cords by approximating the 

 arytenoid cartilage to the thyroid cartilage. This portion of the 

 muscle is, therefore, the antagonist of the crico- thyroid. It is to 

 be borne in mind, however, that one factor in relaxation of the true 

 vocal cords must of necessity be elastic recoil. The fibres represent- 

 ing the ary-vocalis muscle of Ludwig act, according to him, by 

 rendering tense that part of the true vocal cord which is in front of 

 them, and relaxing the part behind them. 



(2) External Portion. In virtue of its insertion into the muscular 

 process of the arytenoid cartilage this portion will draw forwards 

 that process, the effect of which is to swing inwards the vocal 

 process. The fibres known as the thyro-epiglottideus have been 

 supposed to assist in depressing the epiglottis. 



The outer portion of the muscle lies within the ala of the thyroid 

 cartilage. Its lower border is contiguous to the lateral crico- 

 arytenoid, and its upper fibres lie on the outer wall of the ventricle 

 and saccule. The inner portion of the muscle is in close contact 

 with the outer side of the true vocal cord. 



Arytenoid. — The arytenoid muscle lies across the posterior sur- 

 faces of the arytenoid cartilages. It consists of two parts — super- 

 ficial and deep. The superficial part is composed of two decussating 

 bundles, each of which is known as the arytenoideus obliquus; and 

 the deep part constitutes the arytenoideus transversus. 



Arytenoideus Obliquus. — Each of these muscles, which has the 

 form of a narrow oblique bundle, arises from the back of the mus- 

 cular process of the arytenoid cartilage. Its direction is upwards 

 and inwards, and at the median line it decussates with its fellow of 

 the opposite side, thus X. Having reached the summit of the 

 opposite ar5d;enoid cartilage, a few of the fibres terminate upon it, 

 but the majority enter the corresponding aryteno-epiglottidean fold. 

 Being reinforced by a few fibres from the summit of the arytenoid 

 cartilage, the fibres now constitute the aryteno-epiglottideus muscle, 

 which passes forwards within the aryteno-epiglottidean fold to be 

 inserted into the side of the epiglottis. Associated with the aryteno- 

 epiglottideus there are those fibres of the external portion of 

 the thyro-arytenoid muscle which are known as the thyro-epiglot- 

 tideus. 



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



Action. — The two muscles, having the arytenoid cartilages within 

 their embrace, sweep these cartilages together, in which action they 

 are aided by the transverse arytenoid muscle, and the superior aper- 

 ture of the larynx is narrowed, very much after the manner of a 

 sphincter muscle. 



Arytenoideus Transversus. — The fibres of this muscle extend trans- 

 versely from the posterior surface and outer border of one arytenoid 

 cartilage to the posterior surface and outer border of the other 



