490 



MANUAL OF PHYSIOLOGY. 



are those concerned in the act of relaxation when the cords are 

 active. They pull forward the arytenoid cartilages, and at the 

 same time draw the upper part of the cricoid slightly forward. 

 Moreover, these muscles have an all-important action in adapting 

 the edges of the cords and the neighboring surfaces to the exact 

 shape most advantageous to their vibration. 



The stretching of the vocal cords is caused by the contraction 

 of one muscle, the crico-thyroid, which, on the outer side of the 

 larynx, passes downward and forward from the lower part of 



FIG. 198. 



FIG. 199. 



FIG. 198. Diagram of the side view of the larynx showing the position of the vocal 

 cords (v). (Huxley.) Ar. Arytenoid cartilage. Hy. Hyoid bone. Th. Thyroid carti- 

 lage. . Cr. Cricoid cartilage. Tr. Trachea. C.th. Crico-thyroid muscle. Th.A. Thyro- 

 arytenoid muscle. Ep. Epiglottis. 



FIG. 199. Diagram of the opening of the larynx from above. (Huxley.) Th. Thyroid 

 cartilage. Cr. Cricoid cartilage. Ary. Superior extremities of the arytenoid cartilages. 

 V. Vocal cords. Th.A. Thyro-arytenoid muscles. C.a.l. Lateral crico-arytenoid muscle. 

 C.a.p. Posterior crico-arytenoid muscle. Ar.p. Posterior arytenoid muscle. 



the thyroid to the anterior part of the cricoid cartilage. It thus 

 pulls the anterior part of the cricoid cartilage upward, causing 

 it to rotate round an axis passing through its thyroid joints. The 

 upper part of the cricoid, which carries the arytenoids, is thus 

 removed from the anterior attachment of the vocal cords, and 

 the membranes are put on the stretch. 



The requirements necessary for the production of voice are the 

 following : 



