ACTION OF THE LARYNGEAL MUSCLES. 



511 



phonation, but the secretion of their numerous mucous glands moistens the true 

 vocal cords. 



The obliquely directed under-surface of the vocal cords causes the cords to come together very 

 easily when the glottis is narrow during respiration (e.g., in sobbing), while the closure may be 

 made more secure by respiration. The opposite is the condition of the false vocal cords, which, 

 when they touch, are easily separated during inspiration ; while during expiration, owing to the 

 dilatation of the ventricles of Morgagni, they easily come together and close (Wyllie, L. Brun- 

 ton and Cash). 



II. Action of the Laryngeal Muscles. These muscles have a double function : 

 1. One connected with respiration, in as far as the glottis is widened and 



lng.crfc 

 traiQu 



Fig. 352. Fig. 353. 



Fig. 352. Larynx from the front, with the ligaments and the insertions of the muscles. 

 O.K., Os hyoideum; C.th., Cart, thyreoidea; Corp. trit., Corpus triticeum ; C.c, Cart, 

 cricoidea ; C.tr., Cart, tracheales ; Lig. thyr.-hyoid. med., Ligamentum thyreo-hyoideum 

 medium ; Lig. th. -h. lat. , Ligam. thyreo-hyoideum laterale ; Lig. , eric. thyr. med. , Ligam. 

 crico-thyreoideum medium; Lig. cric.-trach., Ligam. crico-tracheale ; M. St.-h., Muse, 

 sterno-hyoideus ; M. th.-hyoid., Muse, thyreo-hyoideus ; M. st.-th., Muse, sterno-thyreo- 

 ideus ; M. cr.-th., Muse, crico-thyreoideus. Fig. 353. Larynx from behind after removal 

 of the muscles. E., Epiglottis cushion (W.) ; L. ar.-ep., Lig. ary-epiglotticum ; M.m., 

 Membrana mucosa; C.W., Cart. Wrisbergii ; C.S., Cart. Santorini ; C. aryt., Cart, 

 aryteenoidea ; C.c., Cart, cricoidea ; P.m., Processus muscularis of Cart, arytam. ; L. cr.-ar., 

 Ligam. crico-aryteean. ; C.s., Cornu superius ; C.i., Cornu inferius Cart, thyreoidea. 

 L. ce.-cr. p. %., Lig. kerato-cricoideum. post, inf.; C.tr., Cart, tracheales; P.m.tr., Pars 

 membranacea tracheae. 



narrowed alternately during respiration ; further, when the glottis is firmly closed 

 by these muscles, the entrance of foreign substances into the larynx is prevented. 

 The glottis is closed immediately before the act of coughing ( 120). 2. The 

 larnyngeal muscles give the vocal cords the proper tension and other conditions for 

 phonation. 



1. The glottis is dilated by the action of the posterior crico-arytenoid muscles. 

 When they contract they pull both processus musculares of the arytenoid cartilages 



