338 Mr Willis oh the 



The two arytenoids are moreover united by a muscle, called 

 the transversus aryteno'ideus, which arises from R d of one ary- 

 tenoid, and is united to the other in the corresponding points. Its 

 section is seen at * in Figs. 2 and 3. It is removed in all the other 

 figures. Its action upon the arytenoids is plainly to press together 

 the point S and its corresponding one. Hence, when this muscle 

 acts at the same moment with the cricoarytenoidei laterales, which 

 we have been just considering, their joint effect will press the whole 

 of the adjacent faces of the arytenoids together, depressing the 

 points V and closing the glottis, and, therefore, antagonizing the 

 action of the cricoarytenoi'deus posticus. (Vide Note E.) 



Indeed, it appears at once from the diagram that the forces NX 

 NY of these two muscles must together produce a resultant in the 

 direction nearly of WN, and therefore directly opposed to the action 

 of the cricoarytenoideus, which is represented in direction by NW. 



Hence, the cricoarytenoidei postici open the glottis. The crico- 

 arytenoidei laterales and the arytenoideus transversus acting jointly 

 close the glottis. 



The complete closing of that portion of the aperture which is 

 included between T and V, (Fig. 8,) appears to be effected jointly 

 by the motion of the arytenoid cartilages, which in closing together 

 approach the point T, from the obliquity of their axjs of motion, 

 and by the swelling of the muscle NX in contracting to bring the 

 arytenoids in contact ; both causes tending- to compress the cellular 

 tissue and muscular fibres which occupy the space TXNV, and 

 therefore to close tightly together the sides of the passage below 

 the vocal ligaments. 



We have now to consider the means by which the vocal ligaments 

 are placed in the proper relative position for vibration. To explain 

 this, let (Fig. 6,) the continued line be the ordinary position of the 



