CHAP, vii.] SPECIAL MUSCULAR MECHANISMS. 1447 



Each arytenoid cartilage is in form an irregular pyramid with 

 the base seated on the cricoid, with the apex directed vertically, 

 but somewhat obliquely, upwards, and with the three surfaces 

 looking one towards the middle line and its fellow, one backwards, 

 and one outwards and forwards. The median surface is not so 

 tall as the other two so that the top of the pyramid appears as it 

 were pinched into a plate, which is irregularly curved, and to the 

 summit of which is attached a nodule of cartilage in the shape of 

 a minute horn, the cartilage of Santorini, or corniculum laryngis 

 (Fig. 181 $.). All the three surfaces are somewhat concave but 

 more or less irregular. 



The hind part of the irregularly triangular base is hollowed 

 out into a small elliptical articular surface for articulation with 

 the cricoid, the long axis of the ellipse being placed transversely. 

 The rest of the base projects beyond the cricoid, and at the front 

 angle, between the median and outer sides, forms a process which 

 is important since it serves for the attachment of the vocal 

 cord, and hence is called the 2^ocessus vocalis (Fig. 181 p.v.)\ 

 the two vocal cords stretch from the two processus vocales, across 

 the larynx to the thyroid, to the re-entering rounded angle of 

 which they are attached at a level which is somewhat nearer the 

 lower than the upper border of the cartilage. The outer angle of 

 the base of the arytenoid between the outer and hind surfaces 

 also forms a process which, since it serves for the attachment of 

 muscles, is called the processus muscularis (Fig. 181 p.m.}; but 

 the remaining angle of the base, that between the median and 

 hind surfaces, is rounded off and does not form any projection. 

 The greater part of the body of the arytenoid is above the level 

 of the vocal cord, since the processus vocalis to which this is 

 attached, though tilted somewhat upwards, is part of the base of 

 the pyramidal cartilage. 



While the movements of the cricoid and the thyroid on each 

 other are on the whole simple in character, the articular surface of 

 the arytenoid permits that cartilage to execute very varied move- 

 ments. Of these the most important, as we shall see later on in 

 detail, are on the one hand a movement of rotation by which the 

 processus vocales converge towards or diverge from each other and 

 the middle line, carrying with them in each case the vocal cords, 

 and on the other hand a movement by which the bodies of the two 

 cartilages are drawn close together in the middle line or dragged 

 far apart. It is by means of these movements and by means of 

 the movement of the cricoid on the thyroid that the changes in 

 the shape and condition of the rima glottidis, upon which the 

 formation of the voice so largely depends, are in the main 

 brought about. 



902. The hind and outer surfaces of the arytenoid pyramid 

 are imbedded in muscular and connective tissue, but the only 

 covering of the median surface is a mucous membrane continuous 



