THE LARYNX 333 



into the ary-epiglottic fold. There they receive the 

 name of the ary-epiglotticus muscle, and, as they approach 

 the epiglottis, they are joined by the fibres of the thyreo- 

 epiglotticus muscle. The oblique arytaenoid muscles may 

 be considered as constituting a weak sphincter muscle 

 for the superior aperture of the larynx. Each bundle 

 starts from the base of one of the arytaenoid cartilages and is 

 prolonged into the ary-epiglottic fold of the opposite side, 

 and onwards, along the fold, to the margin of the epiglottis. 



The arytcenoideus transversus is an unpaired muscle. It is 

 composed of transverse fibres which bridge across the interval 

 between the two arytaenoid cartilages and are attached to 

 the posterior aspect of the lateral border of each arytaenoid 

 cartilage. Many of the fibres turn round the arytaenoid 

 cartilage and become continuous, on each side, with the fibres 

 of the thyreo-arytaenoid muscle. Both groups of fibres are 

 supplied by the inferior laryngeal nerves. The oblique 

 fibres form "a weak sphincter of the superior laryngeal 

 aperture. The transverse fibres adduct the arytaenoid 

 cartilages and abduct the vocal folds. 



Dissection. The further dissection of the laryngeal muscles 

 should be confined to the left side of the larynx. The right 

 side should be reserved for the study of the nerves and vessels. 

 Place the larynx on its right side, and, having fixed it in that 

 position, remove the left crico-thyreoid muscle. The left 

 lateral part of the thyreo-hyoid membrane should next be 

 divided, and the left inferior cornu of the thyreoid cartilage 

 disarticulated from its facet on the side of the cricoid cartilage. 

 An incision should now be made through the left lamina of the 

 thyreoid cartilage, a short distance to the left side of the median 

 plane, and the detached piece must be carefully removed. Three 

 muscles are now exposed, and must be cleaned. They are 

 named, from below upwards : 



1. The lateral crico-arytaenoid. 



2. The thyreo-arytaenoid. 



3. The thyreo-epiglotticus. 



Musculus Crico-arytsenoideus Lateralis. Each lateral 

 crico-arytaenoid muscle is triangular in form, and smaller 

 than the posterior crico-arytaenoid (Fig. 124). It springs 

 from the upper border of the arch of the cricoid cartilage, 

 extending to the facet on the lamina which supports the 

 base of the arytaenoid cartilage; a few of its fibres take 

 origin from the conus elasticus also. From its lower attach- 

 ment its fibres run backwards and upwards, and converge 



