THE LARYNX 335 



(Fig. 118). The mucous membrane is tightly bound down 

 to the vocal ligament and, in this situation, it contains very 

 few blood-vessels. On this account the vocal folds are much 

 paler in colour than the surrounding mucous membrane 

 under normal conditions. 



In the vestibule and ventricle of the larynx, the mucous 

 membrane is very loosely bound down, except over the 

 epiglottis and the vocal folds. In oedema glottidis, serum 

 collects in the loose submucous tissue of the larynx and 

 gravitates downwards. It cannot, however, descend over the 

 vocal folds, and consequently, as it increases in amount, it 

 brings the ventricular folds (false cords) and the walls of the 

 cavity into contact with one another, causing complete 

 obstruction to respiration. 



The vocal ligament is attached to the thyreoid angle in 

 front and to the vocal process (anterior basal angle) of the 

 arytaenoid behind. Under favourable conditions, the vocal 

 process can be seen in the posterior part of the vocal fold on 

 laryngoscopic examination. 



The rima glottidis consists of an intermembranous part, 

 placed between the vocal folds, and an intercartilaginous part, 

 placed between the vocal processes and the bases of the 

 arytaenoid cartilages (Fig. 120). The differentiation into two 

 parts is seen best when the glottis is widely open, as it then 

 assumes a somewhat lanceolate shape. This shape is assumed 

 because the arytaenoid cartilages, being unable to separate 

 widely from one another, undergo rotation on the cricoid so 

 that the vocal processes are rotated laterally (Fig. 120). 



The muscles which act on the vocal folds may be divided 

 into four groups (a) Tensors, (b) relaxors, (c) abductors, and 

 (d) adductors. 



(a) The crico-thyreoid passes backwards and upwards from 

 the side of the cricoid to the thyreoid cartilage. The line of 

 its pull lies in front of the crico-thyreoid joint, and conse- 

 quently, when the muscle contracts, it tilts the thyreoid 

 cartilage downwards and forwards. As a result, the anterior 



