1074 THE EESPIKATOKY SYSTEM. 



The nerve supply is the anterior branch of the inferior laryngeal nerve. 



The m. arytaenoideus transversus is a thick, oblong, unpaired muscle which lies 

 in the dorsal wall of the larynx and bridges across the interval between the two 

 arytaenoid cartilages. The ventral surface of the muscle is in contact with the 

 dorsal concave surfaces of the arytaenoid cartilages, and between them with the 

 mucous membrane of the larynx. Its dorsal surface is partly concealed by the 

 arytaenoidei obliqui and by the submucous tissue of the pharynx. The inferior 

 border extends to the lamina of the cricoid cartilage, and its upper border does not 

 quite reach the apices of the arytaenoid cartilages. 



The attachments of the muscle are, on both sides, to the dorsal surface of the 

 processus muscularis and the lateral edge of the arytaenoid cartilages. All the fibres 

 run in a frontal (coronal) direction, and some turn round the arytaenoid cartilage 

 to become continuous with the thyreo-arytaenoideus. The arytaenoideus trans- 

 versus and the thyreo-arytaenoid muscles form, together, a sphincter of the glottis. 



By its action the arytaenoideus transversus approximates the arytaenoid 

 cartilages, thereby tending to close the pars intercartilaginea of the rima glottidis. 

 Its assistance in the sphincter action of the thyreo-arytaenoideus has already 

 been pointed out. 



The' muscle is innervated by the posterior or dorsal rami of the inferior 

 laryngeal nerve of both sides. 



The mm. arytaenoidei obliqui are a pair of muscles which lie in the dorsal wall 

 of the larynx, immediately dorsal to the arytaenoideus transversus and ventral 

 to the submucous tissue of the pharynx. 



Each muscle consists of a bundle of muscular fibres which arise from the 

 dorsal aspect of the processus muscularis of the corresponding arytaenoid cartilage. 

 From their origins the two fleshy slips proceed upwards and medially, and cross 

 each other in the median plane like the two limbs of the letter X. Beaching 

 the apex of the arytaenoid cartilage of the opposite side, many, but not all, of the 

 fibres are inserted there, but others receiving a fresh attachment arise from the 

 apex of the arytaenoid cartilage as the m. aryepiglotticus, and extend ventrally and 

 upwards in a series of arches within the aryepiglottic fold to terminate in the 

 thyreo-epiglottic ligament and the lateral margin of the epiglottic cartilage ; and as 

 the muscle approaches the latter structure its fibres are joined by the fibres of the 

 thyreo-epiglotticus. With its superior border are also commingled some fibres 

 from the m. stylo-pharyngeus. 



Action. The arytaenoideus obliquus and aryepiglotticus combined, act as a 

 rudimentary sphincter muscle for the aditus and the vestibulum laryngis, that is 

 for the superior aperture of the larynx, inasmuch as they extend from the base of 

 one arytaenoid cartilage to the apex of the arytaenoid cartilage of the opposite side, 

 and then on to the epiglottis within the ary-epiglottic fold. 



The two muscular slips are innervated by the corresponding anterior rami 

 of the inferior laryngeal nerves. 



The mm. cricoarytsenoidei posteriores are a pair of triangular muscles, each of 

 which lies on the dorsal surface of the lamina of the cricoid cartilage, under cover 

 of the tela submucosa of the pharynx. Each arises, by a broad origin, from the 

 medial and inferior* part of the depression on the dorsal surface of the lamina of 

 the cricoid cartilage at the side of the median ridge ; from that origin its fibres 

 converge upwards and laterally to be inserted into the dorsal surface and apex 

 of the processus muscularis of the corresponding arytaenoid cartilage. In 

 their course from origin to insertion the muscular fibres display very different 

 degrees of obliquity. The most superior fibres are short and nearly horizontal ; the 

 intermediate fibres are the longest and are very oblique ; whilst the most inferior 

 fibres are almost vertical in their direction. 



By its action the crico-arytaenoidei posteriores draw the muscular processes 

 of the arytaenoid cartilages medially and dorsally, swing the vocal processes and 

 the vocal folds laterally, and thereby open the rima glottidis. 



The muscle is innervated by the posterior ramus of the inferior larynge* 

 nerve. 



The mm. thyreoepiglottici are a pair of thin, oblong, very variable muscles ; 



