THE ARYTESOID MUSCLES. 691 



part of the posterior surface of the arytenoid cartilage. On its hinder 

 surface lie the aryteno-epiglottidean muscles ; and the laryngeal 

 mucous membrane covers it in front in the space between the 

 cartilages. 



Action. It draws together the arytenoid cartilages, rendering use. 

 narrower the opening of the glottis. 



The ARYTENO-EPIGLOTTIDEAN MUSCLES (A) are tWO small bundles Aryteno- 



which cross obliquely from one side to the other on the back of the Jean^mSs- 

 arytenoid muscle. Each arises from the outer and lower part of ^ s cross 

 the posterior surface of one arytenoid cartilage, and passes to the x : 

 upper part of the outer border of the cartilage of the opposite side, 

 where a few of the fibres are inserted, but the greater number turn 

 round this border and end in the aryteno-epiglottidean fold of the 

 mucous membrane, some reaching the margin of the epiglottis. A 

 slip is also prolonged into the thyro-arytenoid muscle. The ending 

 of the muscle will be seen later when the ala of the thyroid cartilage 

 has been removed. 



Action. These muscles bring together the tips of the arytenoid use. 

 cartilages, and depress the epiglottis, thus assisting to close the 

 upper aperture of the larynx in swallowing. 



Dissection. The remaining muscles (fig. 246, p. 692) will be Dissection 

 brought into view by removing the greater part of the right ala of muscles"* 1 

 the thyroid cartilage, by cutting through it a quarter of an inch from 

 the middle line, alter its lower cornu has been detached from the Remove half 

 cricoid, and the crico-thyroid muscle taken away. By dividing next cartilage, 

 the thyro-hyoid membrane attached to the upper margin, the loose 

 piece will come away on separating the subjacent areolar tissue 

 from it. 



By the removal of some areolar tissue, the dissector will define Position of 

 inferiorly the lateral crico-arytenoid muscle ; above it, the thyro- m 

 arytenoid muscle ; and still higher, the pale fibres of the aryteno- 

 epiglottidean and thyro-epiglottidean muscles in the fold of mucous 

 membrane between the epiglottis and the arytenoid cartilage. On 

 cleaning the fibres of the thyro-arytenoid near the front of the 

 larynx, the top of the sacculus laryngis with its small glands will 

 appear above the fleshy fibres. 



The LATERAL CRICO-ARYTENOID MUSCLE (fig. 246, s ) arises from Lateral 



the upper border of the cricoid cartilage at the side, and is directed arytenoid 

 backwards to be inserted into the fore part of the muscular process of muscle : 

 the arytenoid cartilage. It is concealed by the crico-thyroid muscle 

 and the thyroid cartilage, and its upper border is contiguous to the 

 succeeding muscle. 



Action. It rotates inwards the arytenoid cartilage, opposing the use. 

 posterior crico-arytenoid muscle, and bringing one vocal cord to the 

 other, so as to narrow the glottis. 



The THYRO-ARYTENOID MUSCLE (fig. 246, 4 ) extends from the thyroid Thyro-ary- 

 to the arytenoid cartilage ; it is thick below, but thin and expanded muscle 

 above. The muscle arises from the thyroid cartilage near the middle 

 line, for about the lower half of its depth, and from the crico-thyroid 



y r 2 



