THE LARYNX 65 



arytenoideus muscle, and to the outer surface the thyro-arytenoideus 

 muscle is attached. The base presents a small shallow facet for 

 articulation with the cricoid. The apices project upwards and 

 backwards, and correspond to the cornicula laryngis or man. 



The above cartilages are attached to one another in a manner which 

 permits of a great degree of movement and flexibility. 



The vocal cord is the upper edge of the thyro-arytenoid ligament, 

 which runs from the anterior edge at the base of the arytenoid cartilage, 

 to the back of the body of the thyroid, and the necessary tension and 

 parallelism of the edges of the cord for the production of sound, are 

 brought about by the movements of the arytenoid cartilages upon 

 the cricoid. The articulation between these cartilages is of great 

 importance, and will be concerned in an operation to be described 

 hereafter, in which one of the arytenoid cartilages is excised. The 

 concave facet, already mentioned, on the base of the arytenoid cartilage 

 accommodates a convex articular surface on the upper aspect of the 

 cricoid. The joint is ot the diarthrodial variety, and possesses a small 

 capsular ligament which is lined by a synovial membrane. 



Muscles of the Larynx. — The muscles of the larynx are in two 

 groups, extrinsic and intrinsic. 



The extrinsic group includes the sterno-thyro-liyoideus and the hyo- 

 epiglottideus muscles. The attachment and action of the latter have 

 already been given. 



The sterno-thyro-hyoideus muscle arises from the cariniform catilage 

 of the sternum. It is a long ribbon- like muscle, which extends up 

 the neck along the inferior surface of the trachea, being closely applied 

 in the middle line to its fellow of the opposite side. 



In the upper part of the neck the muscle divides into two portions^ 

 one of which continues its course along the trachea to be inserted into 

 the body of the hyoid bone, whilst the outer division runs to its 

 insertion into the thyroid cartilage. 



The intrinsic group is made up of four pairs and one single muscle. 



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