334 Mr Willis on the 



and BF, Fig. 3, diverging from the point B, Fig. 8, which point 

 B is as nearly as possible the point where the axis of the articu- 

 lating surface would intersect the cricoid. The vocal ligament 

 is stretched from the thyroid at T to the arytenoid at V, and as 

 there is no muscle which can relax the ligament BRS*, it re- 

 ceives and transmits to the point B of the cricoid the tension of 

 the vocal ligaments. 



The motion of the arytenoid is therefore compounded of a rota- 

 tion round the axis OP, and of a sliding motion transverse to 

 this axis, which is confined by the tension of BRS to a swinging 

 round the point B, of which we shall presently see the use. 



We have already seen that the thyroid is so united to the 

 cricoid as to turn round the point C, Figs. 3 and 4, as a fulcrum. 

 The effect of this rotation is to alter the distance between the point 

 E of the thyroid, and B of the cricoid, and therefore to affect 

 the tension of the vocal ligaments. 



If this distance be increased by the thyroid revolving in the 

 direction from B to E, the tension of the vocal ligament is in- 

 creased, and by its pulling at the arytenoid cartilage the tension 

 of the bundle of ligaments is increased. If the distance EB be 

 diminished by the thyroid turning in the reverse direction, the 

 contrary effect will take place. 



To produce this motion, two pair of muscles are provided, 

 one of the external pair (the cricothyroid muscle) is seen at AK, 

 Fig. 4f, when this muscle contracts it brings the point K of the 



* Vide Note C 



+ Each muscle of this pair is sometimes seen divided into two, and is described by 

 some writers as such. Some of the fibres are attached so close to the fulcrum C as to be 

 apparently intended to stretch the ligaments which bind the horns C of the thyroid to the 

 cricoid, and thereby unite more firmly these two cartilages during vocalisation. 



