132 SURGICAL APPLIED ANATOMY. [Chap. ix. 



The thyroid and cricoid cartilages, and the greater 

 part of the arytenoid, are in structure hyaline, as are 

 the costal cartilages. Like the last-named, they are 

 liable to become more or less ossified as life ad- 

 vances, and when ossified are liable to be fractured 

 by violence ; the cartilage usually so fractured is the 

 thyroid. 



The rim a. glottidis is the aperture between the 

 true vocal cords in front and the bases of the arytenoid 

 cartilages behind. It is the narrowest part of the 

 interior of the larynx, and it is well to be familiar 

 with its proportions in reference to the entrance of 

 foreign bodies, and the introduction of instruments. 

 In the adult male the rima measures nearly one inch 

 (23 millimetres) from before backwards ; from side 

 to side, at its widest part, it measures about 8 mm., 

 and this diameter may be increased to 12 mm. in 

 extreme dilatation. In the female and the male before 

 puberty the antero-posterior diameter is about 17 mm., 

 and the transverse about 4 mm. 



The mucous membrane of the larynx varies 

 in thickness in different parts, and in the amount of 

 its submucous tissue. The membrane is thickest, and 

 the submucaus tissue most abundant, in the following 

 parts, taken in order of degree : The aryteno- 

 epiglottic(ean folds, the mucous membrane of the 

 ventricle, the fajse cords, and the laryngeal aspect of 

 the epiglottis. These are the parts that become 

 most congested and swollen in acute laryngitis ; and 

 the serious condition known as oedema of the glottis 

 depends mainly upon effusion into the lax submucous 

 tissue in the aryteno-epiglottidean folds. The affection 

 known as " clergyman's sore-throat " has an interesting 

 anatomical basis. The mucous membrane of the 

 larynx is well provided with mucous glands, whose 

 function it is to keep moist the parts concerned in 

 phonation. When an individual speaks aloud for a 



