MUSCLES OF THE LARYNX 



1219 



strictors. They form a ring, the constrictor laryngis, around the laryngeal cavity, 

 interrupted, however, by the cartilages. In the larynx of amphibia and reptiles 

 a complete sphincter guards the entrance to the air-passages. 



The following muscles are included in the constrictor group: — 

 The transverse arytaenoid muscle [m. arytsenoideus transversus] (figs. 981) 

 983, 985) is a single muscle of quadrilateral form, extending across the middle 

 line from the posterior concave surface of one arytgenoid cartilage to that of the 

 other. Its anterior surface, between the cartilages, is covered by the laryngeal 

 mucosa; its posterior surface, crossed by the arytsenoideus obhquus, is clothed by 

 the submucous coat of the pharynx. 



The arytaenoideus transversus approximates the arytsenoid cartilages and their vocal proc- 

 esses, which are at the same time elevated, and the vocal Hgaments made tense. It is supphed 

 by the posterior branch of the inferior laryngeal nerve. 



Fig. 985. — The Nerves of the Larynx seen from Behind. 



Greater cornu of hyoid 

 Triticeous cartilage 



Ary-epiglottic fold 

 Superior cornu of 

 thyreoid 

 Corniculate cartilage 



Anterior branch of in- 

 ferior laryngeal nerve 



Posterior branch of in- 

 ferior laryngeal nerve 

 Posterior crico-arytae- 

 noid muscle 



Crico-thyreoid joint 



Base of the tongue 



Epiglottis 



External branch of su- 

 perior laryngeal nerve 



Internal branch of su- 

 perior laryngeal nerve 



Cut edge of hyo-thy- 

 reoid membrane 



Cuneiform tubercle 



Oblique arytaenoid 

 Arytsenoid cartilage 



Lamina of cricoid 



Inferior laryngeal 

 nerve 



The lateral crico -arytaenoid muscle [m. cricoarytsenoideus lateralis] (fig. 981) 

 arises from the upper margin and outer surface of the cricoid arch and from the 

 elastic cone, whence the fibres extend backward and upward to an insertion on 

 the anterior surface of the muscular process of the arytaenoid cartilage. This 

 muscle is inseparable from the thyreo-arytsenoideus in about half the cases. 



The lateral cricoarytaenoids by their contraction cause the vocal processes to move toward 

 the median hne and a little downward, so that the vocal hgaments are approximated and slightly 

 stretched. They antagonise the posterior crico-arytsenoids. The anterior branch of the in- 

 ferior laryngeal nerve supplies these muscles. 



The external thyreo-arytaenoid muscle [m. thyreoarytaenoideus (externus)] 

 (figs. 981, 984, 988), variable in form and in the disposition of its fibres, is closely 

 connected with the preceding. It lies under cover of the thyreoid lamina lateral 

 to the laryngeal saccule (ventricular appendix) and elastic cone. Arising within 

 the angle of the thyreoid laminae the muscle extends upward and backward to its 

 insertion on the lateral margin of the arytaenoid cartilage. 



