TENSION CHANGES IN VOCAL CORDS. 601 



and brought into its state in deep quiet breathing. Other 

 muscles approximate the arytenoid cartilages after they 

 have been separated. The most important is the transverse 

 arytenoid (A, Fig. 158), which runs across from one ary- 

 tenoid cartilage to the other. Another is the oblique ary- 

 tenoid (Taep], which runs across the middle line from the 

 base of one arytenoid to the tip of the other; thence cer- 

 tain fibres continue in the aryteno-epiglottidean fold (10, 

 Fig. 157) to the base of the epiglottis; this, with its fellow, 

 thus embraces the whole entry to the larynx ; when they 

 -contract they bend inwards the tips of the arytenoid car- 

 tilages, approximate the edges of the aryteno-epiglottidean 

 fold, and draw down the epiglottis, and so close the pas- 

 sage from the pharynx to the larynx. When the epiglottis 

 has been removed, food and drink rarely enter the larynx 

 in swallowing, the folds of mucous membrane being so 

 brought together as to effectually close the aperture be- 

 tween them. 



Increased tension of the vocal cords is produced by the 

 trico-thyroid muscles, one of which lies on each s : ie of the 

 larynx, over the crico-thyroid membrane. Their action 

 may be understood by help of the diagram, Fig. 159, in 

 which t represents the thyroid 

 cartilage, c the cricoid, a an f\ 

 Arytenoid, and vc a vocal cord. 

 The muscle passes obliquely 

 backwards and upwards from 

 About d near the front end of 

 4, to t, about I, near the pivot 

 (which represents the joint be- 

 tween the cricoid cartilage and 

 the inferior horn of the thy- 

 roid). When the muscle con- 

 tracts it pulls together the ante- 

 rior ends of t and c; either by depressing the thyroid (as 

 represented by the dotted lines) or by raising the front 

 -end of the cricoid; and thus stretches the vocal cord, 

 if the arytenoid cartilages be held from slipping 

 forwards. The antagonist of the crico-thyroid is the 



