404 SPLANCHNOLOGY, OR ANATOMY OF THE VISCERA 



outer surface of the arytenoid cartilage; its outer part, into 

 the outer border and muscular process of the same cartilage, 

 above the internal part. The internal part is adherent and 

 parallel to the true vocal cord; the outer is external to the 

 sacculus laryngis. Their action is to advance the arytenoid 

 cartilages and thus relax the vocal cords. The nerve comes 

 from the inferior laryngeal. 



The thyrocpujlotticus muscle consists of a considerable number 

 of the fibers of the thyroarytenoideus prolonged into the aryteno- 

 epiglottic fold, where some of them become lost, others pass 

 on to the margin of the epiglottis. 



The posterior cricoarytenoid arises from the broad depres- 

 sion occupying each lateral half of the posterior surface of 

 the cricoid cartilage; its fibers pass upward and outward, con- 

 verging to be inserted into the outer angle (muscular process) 

 of the base of the arytenoid cartilage. The upper fibers are 

 nearly horizontal, the middle, oblique, and the lower almost 

 vertical. 



The lateral cricoarytenoid arises from the upper border of the 

 side of the cricoid cartilage, and is inserted into the muscular 

 process of the arytenoid cartilage in front of the posterior 

 cricoarytenoid muscle. 



The arytenoid is a single muscle occupying the posterior 

 concave surface of the arytenoid cartilage, and is inserted 

 into the corresponding parts of the opposite cartilage'. It 

 consists of an oblique and transverse set of fibers, the former 

 arranged like the limbs of the letter X, the latter fibers pass 

 transversely across. A few of the oblique fibers are continued 

 around the outer margin of the cartilage, and blend with the 

 thyroarytenoid muscle in the arytenoepiglottic fold, and are 

 called the aryepiglotticus muscle. 



Actions of the intrinsic muscles: (1) Those which open 

 and close the glottis. (2) Those which regulate the degree 

 of tension of the vocal cords. 



1. The two posterior cricoarytenoids open the glottis; and 

 the arytenoid and the two lateral cricoarytenoids close it. 



2. The two cricothyroids regulate the tension of the vocal 

 cords, and elongate them by the same action; the two thyro- 

 arytenoids relax and shorten them. 



The posterior cricoarytenoids separate the vocal cords, 

 and consequently open the glottis, by rotating the arytenoid 



