512 



ACTION OF THE LARYNGEAL MUSCLES. 



backwards, downwards, and towards the middle line (fig. 356), so that the processus 

 vocales (I, I) must go apart and upwards (II, II). Thus, between the vocal cords 

 (glottis vocalis), as well as between the inner margins of the arytenoid cartilages, 

 a large triangular space is formed (glottis respiratoria), and these spaces are so 

 arranged that their bases come together, so that the aperture between the cords and 

 the arytenoid cartilages has a rhomboidal form. Fig. 356 shows the action of the 

 muscles. The vocal cords, represented by lines converging in front, arise from the 

 anterior angle of the arytenoid cartilages (I, I). When these cartilages are rotated 



Lornu 



Fig. 354. Fig. 355. 



Fig. f 354. Larynx from behind with its muscles. E., Epiglottis, with the cushion (W.) ; 

 C.W., Cart. Wrisbergii ; C.S., Cart. Santorini ; C.c, Cart, cricoidea. Cornu sup. 

 Cornuinf., Cart, thyreoklene ; M. ar. tr., Muse, arytenoideus transversus ; Mm. ar. obi., 

 Musculi aryt;enoidei obliqui ; M. cr.-aryt. post., Musculus crico-arytsenoideus posticus ; Pars 

 cart., Pars cartilaginea ; Pars memb. , Pars membranacea tracheae. Fig. 355. Nerves of 

 the larynx. O.h., Os hyoideum ; C.th., Cart, thyreoidea ; C.c, Cart, cricoidea; Tr., 

 Trachea; M. th.-ar., M. thyreo-arytienoideus ; M. cr.-ar. p., M. crico-arytamoideus 

 posticus ; M. cr.-ar I., M. crico-arytam. lateralis; M. cr.-th., M. crico-thyreoideus ; 

 X. lar. sicp. v., N. laryngeus sup. ; R.I., Ramus internus ; R.E., Ramus ext. ; N. lar. rcc. v., 

 N. laryngeus recurrens ; R.I.N.L.R., Ramus int.; R.E.N.L.R., Ramus ext. nervi laryngei 

 recurrentis vagi. 



into the position (II, II), the cords take the position indicated by the dotted lines. 

 The widening of the respiratory portion of the glottis between the arytenoid carti- 

 lages is also indicated in the diagram. 



Pathological. When these muscles are paralysed, the widening of the glottis does not take 

 place, and there may be severe dyspnoea during inspiration, although the voice is unaffected 

 (Riegcl, L. Weber). In a larynx just excised, the dilators are the first to lose their excitability 

 (Semon and Horslcy). 



2. The entrance to the glottis is constricted by the arytenoid muscle (trans- 

 verse), which extends transversely between both outer surfaces of the arytenoids 

 along their whole length (fig. 357). On the posterior surface of this muscle is 



