126 The Ldrynx 



thyroid are hinged at the lower part of the side by capsular ligaments 

 and synovial membranes. 



When more room is needed in tracheotomy it may be expedient to 

 divide the cricoid (vid. inf.}. 



The arytsenoid cartilages are two small pyramids which articu- 

 late by their base with the upper and back part of the cricoid. Of 

 their three surfaces, the inner looks towards its fellow, and is covered 

 by mucous membrane ; the posterior is connected with its fellow by the 

 arytsenoideus, and the anterior receives the insertion of the thyro- 

 arytaenoid muscle. 



To the anterior angle is attached the true vocal cord ; the external 

 angle receives the insertion of muscular slips which arise on the cricoid, 

 and the apex is connected with the corniculum laryngis, which is hidden 

 in the arytaeno-epiglottidean folds. 



The epiglottis, shaped like an obovate leaf, is attached by its stalk 

 to the back of the thyroid, just above the vocal cords ; its anterior 

 surface is connected with the back of the hyoid bone by the hyo-epi- 

 glottic ligament, and with the base of the tongue by three bands of 

 mucous membrane the glosso-epiglottidean folds. The posterior 

 surface looks towards the back of the pharynx during respiration ; but 

 when the larynx is hidden beneath the base of the tongue during de- 

 glutition, and the glosso-epiglottidean folds are relaxed, the epiglottis 

 falls over the laryngeal aperture, and its posterior surface is turned 

 downwards. 



Structure. The epiglottis is composed of yellow fibrp-cartilage, 

 which does not ossify, but the thyroid, cricoid, and arytaenoid cartilages 

 are apt, like the costal cartilages, to ossify as age advances. 



The thyro-hyoid membrane is attached to the upper border of 

 the thyroid cartilage, and, ascending behind the hyoid bone, is con- 

 nected with its upper border, a bursa intervening between the mem- 

 brane and the back of the bone. On rare occasions this bursa be- 

 comes inflamed, or, being distended with fluid, forms a cyst. The 

 bursa is placed there in order that the thyroid cartilage may ascend 

 freely behind the hyoid bone during deglutition. 



Through each side of the membrane run the superior laryngeal 

 vessels and nerve. 



The crico-tnyroid membrane fills the interval between the cricoid 

 and thyroid cartilages, and is firmly connected with them in front ; 

 laterally, however, it ascends free on the inner side of the thyroid, and 

 becomes continuous above with the lower border of the true vocal cord. 

 The anterior part of the membrane is subcutaneous, but its sides are 

 covered by the crico-thyroid muscles. Upon it rests the anastomotic 

 loop between the two crico-thyroid or external laryngeal arteries. 



The membrane is traversed in the operation of laryngotomy, and 

 sometimes the insertion of the tube fails to arrest bleeding from the 

 divided artery. 



