MOVEMENTS OF LARYNX. 599 



contains no glands. In quiet breathing, and after death, 

 the free inner edges of the vocal cords are thick and rounded, 

 and seem very unsuitable for being readily set in vibration. 

 They are also tolerably widely separated behind, the aryten- 

 oid cartilages, to which their posterior ends are attached, 

 being separated. Air under these conditions passes through 

 without producing voice. If they are watched with the 

 laryngoscope during phonation, it is seen that the cords 

 approximate behind so as to narrow the glottis; at the same 

 time they become more tense, and their inner edges project 

 more sharply and form a better-defined margin to the 

 glottis, and their vibrations can be seen. These changes 

 are brought about by the delicately co-ordinated activity of 

 a number of small muscles, which move the cartilages to 

 which the cords are fixed. 



The Muscles of the Larynx. In describing the direc- 

 tion and action of these it is convenient to use the words 

 front or anterior and back or posterior with reference to 

 the larynx itself (that is as equivalent to ventral and dorsal) 

 and not with reference to the head, as usual. The base of 

 each arytenoid cartilage is triangular and fits on a surface 

 of the cricoid, on which it can slip to and fro to some ex- 

 tent, the ligaments of the joint being lax. One corner of 

 the triangular base is directed inwards and forwards (i.e. 

 towards the thyroid) and is called the vocal process (Pv, 

 Fig. 156). as to it the vocal cords are fixed. The outer 

 posterior angle (Pm, Fig. 156) has several muscles inserted 

 on it and is called the muscular process. If it be pulled 

 back and towards the middle line the arytenoid cartilage 

 will rotate on its vertical axis, and roll its vocal processes 

 forwards and outwards, and so widen the glottis; the re- 

 verse will happen if the muscular process be drawn forwards. 

 The muscle producing the former movement is the posterior 

 crico-arytenoid (Cap, Fig. 188); it arises from the back of 

 the cricoid cartilage, and narrows to its insertion into the 

 muscular process of the arytenoid on the same side. The 

 opponent of this muscle is the lateral crico-arytenoid, 

 which arises from the side of the cricoid cartilage, on its 

 inner surface, and passes upwards and backwards to tho 



