CH. LIV.] MUSCLES OF LARYNX. 7 2 9 



are iti a fold of mucous membrane ; the epiglottis looks like a lid to the 

 whole (fig. 551). 



The thyroid cartilage is connected with the cricoid, by the crico-thyroid 

 membrane, and also by joints with synovial membranes ; the lower coriniu 

 of the thyroid clasp the cricoid between them, yet not so tightly but 

 that the thyroid can revolve, within a certain range, around an axis 

 passing transversely through the two joints at which the cricoid is clasped. 

 The vocal cords are attached behind to the front portion of the base 

 (vocal process) of the arytenoid cartilages, and in front to the re-entering 

 angle at the back of the thyroid ; it is evident, therefore, that all move- 



Fig. 552. Vertical section through the larynx, passing from side to side. H, hyoid bone 

 T, thyroid cartilage ; T.C.M., thyro-cricoid membrane ; C, cricoid cartilage ; Tr, tirst 

 ring of trachea ; T.A., thyro-arytenoid muscle ; H.Q., rima glottidis ; V.C., vocal cord ; 

 V, ventricle ; F.V.C., false vocal cord. (After Allen Thomson.) 



ments of either of these cartilages must produce an effect on them of 

 some kind or other. Inasmuch, too, as the arytenoid (Cartilages rest on 

 the top of the back portion of the cricoid criMilage, and are connrctrd 

 with it by capsular and other ligaments, all movements of the cricoid 

 cartilage must move the arytenoid cartilages, and also produce an effi-'-t mi 

 the vocal cords. 



Mucous membrane. The larynx is lined with a mucous membrane 

 continuous with that of the trachea : this is covered with ciliated epithelium 

 except over the vocal cords and epiglottis, where it is stratified. The 

 vocal cords are thickened bands of elastic tissue in this mucous mem- 

 brane which run from before back. They are attached b -hind to the vocal 

 pi ^-'^ f ill'' ;irvtriioid <-:iiiil:i-_'f. ;md in l'i.,m t,, i| M > ;iiiL'l<- u line tin- 

 two wings of tin- thyroid meet. The chink between them is called tin- 

 rinni gluttidi* (see fig. 552). Two ridges of mucous membrane above and 



