496 THE HUMAN BODY 



Other muscles approximate the arytenoid cartilages after the car- 

 tilages have been separated. The most important is the transverse 

 arytenoid (A, Fig. 147), which runs across from one arytenoid car- 

 tilage to the other. Another is the oblique arytenoid (Taep), which 

 runs across the middle line from the base of one arytenoid to the 

 tip of the other; thence certain fibers continue in the aryteno- 

 epiglottic fold (10, Fig. 146) to the base of the epiglottis; this, 

 with its fellow, embraces the whole entry to the larynx; when 

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

 lages, approximate the edges of the aryteno-epiglottic fold, and 

 draw down the epiglottis, and so close the passage 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 between them. 



Increased tension of the vocal cords is produced by the crico- 

 thyroid muscles, one of which lies on each side of the larynx, over 

 the cricothyroid membrane. Their action may be understood 

 by help of the diagram, Fig. 148, in which t represents the thyroid 



cartilage, c the cricoid, a an arytenoid, 

 and vc a vocal cord. The muscle passes 

 obliquely backwards and upwards from 

 about d near the front end of c, to t, 

 about Z, near the pivot (which represents 

 the joint between the cricoid cartilage 

 ^"""^^ TV./ ut and the inferior horn of the thyroid). 

 **"*--O''* ; *' When the muscle contracts it pulls to- 



-~-\ gether the anterior 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 aryte- 

 noid cartilages be held from slipping forwards. The antagonist of 

 the cricothyroid is the thyro-arytenoid muscle; it lies, on each side, 

 embedded in the fold of elastic tissue forming the vocal cord, and 

 passes from the inside of the angle of the thyroid cartilage in front, 

 to the anterior angle and front surface of the arytenoid behind. 

 If the latter be held firm, the muscle raises the thyroid cartilage 

 from the position into which the cricothyroid pulls it down, and so 

 slackens the vocal cords. If the thyroid be held fixed by the 



