348 Mr Willis on the 



view of the action of the current correct, it is manifest that the reed would, 

 after a few oscillations, assume a position of rest in every case. These 

 remarks of mine have suggested to Professor Airy the investigation of an 

 elegant law, for which I must refer to his ingenious paper in the previ- 

 ous volume (p. 369) " On Certain Conditions under which a Perpetual 

 Motion is possible." 



Note C.—Page 337. 



The offices generally assigned to the cricoarytenoideus posticus are to 

 open the glottis by drawing the arytenoid backward, and to stretch the 

 vocal ligament. Now it is perfectly true that this muscle {N1V Fig. 8) 

 in drawing the arytenoid from the mesial plane to open the glottis will 

 affect the tension of the vocal ligament TV by increasing the distance TV. 

 But the only function in which the tension of the ligament is concerned 

 is vocalisation, and for this a pecidiar position of the ligament is required, 

 which is given by the thyroarytenoi'dei,. while the complete and direct 

 regulation of the tension is also provided for by the joint action of the 

 ericothyroidei and thyroarytenoi'dei. On the other hand, the effect of the 

 cricoarytenoideus posticus upon the tension is very slight at the first 

 departure of the point V from the mesial plane, indirect and inconsiderable 

 in every case, and it cannot act without drawing the cartilages asunder 

 and out of the vocalising position ; therefore I infer, that this muscle is 

 never concerned in adjusting the tension for vocalisation, and that its effect 

 upon it may therefore be neglected. 



Again, the phrase " drawing the arytenoid backward," is a loose one, 

 and implies that the ligament BRBS is relaxed by this action, which 

 is by no means the case. I have attempted to shew that this muscle 

 produces rotation round the axis OP; and as the bundle of ligaments 

 radiate from about that point B of the cricoid where the axis intersects 

 its surface, it is plain that the rotation of the arytenoid will scarcely affect 

 their tension. It is true that those fibres of the muscle which lie nearest 



