Mechanism of the Larynx. 337 



The articulation of the arytenoids with the cricoid has been 

 already described. From the extremity N, (Fig. 8,) of the ary- 

 tenoid arises a muscle, termed the cricoaryteno'ideus posticus, which 

 is turned round the edge of the cricoid, and affixed to the lower 

 part of the back of the latter cartilage. Its mechanical action, 

 however, is the same as if it acted on the arm of a short lever N, 

 in the direction NW on the plan, that is to say, perpendicular to 

 the axis of motion OP, and its effect is to produce rotation about 

 this axis, and therefore to separate the arytenoid cartilages from 

 each other and open the passage. (Vide Note C) 



From the arytenoid another muscle NX arises, and is attached 

 to the cricoid at and about the point X; this is termed cricoary- 

 teno'ideus lateralis. In Fig. 3, the fibres of this muscle may be 

 seen arising from X and passing up to the arytenoid, lying nearly 

 parallel to the projection of the axis of motion. 



To understand the action of this muscle upon the arytenoid, 

 we must remember that the latter is attached to the point B by 

 ligaments, which radiate from this point, and are united to the 

 arytenoid along its posterior surface from S to R. 



The tension of this muscle then in the direction NX will, by 

 drawing the cartilage in that direction, stretch the ligament RB. 

 and tend to bring the points XNB into the same straight line ; this 

 will at the same time approximate the point V to the medial plane 

 and corresponding point of the other arytenoid, and also, (as it 

 appears from Fig. 3 that in the vertical projection, N is above 

 the line joining BX,) it will depress N and still more V, because 

 the cartilage turns on the articulating surface beneath Q. 



The effect, in short, of the pair of muscles in question is to press 

 the points V of the arytenoids together, at the same time depressing 

 them. 



