CHAP, vii.] SPECIAL MUSCULAR MECHANISMS. 1073 



If the voice, and especially if a high note, be uttered the 

 view changes (Fig. 187 A) ; besides an alteration in the form of 

 the laryngeal aperture, the vocal cords are seen to be brought 

 close together and nearly parallel so that the glottis becomes a 

 mere slit. If no voice is being uttered and a deep inspiration 

 be taken changes of another kind may be observed (Fig. 187 (7) ; 

 the glottis becomes a wide aperture with the form of a truncated 



Cri.J 



FIG. 186. DIAGRAM OF THE LARYNX IN VERTICAL TRANSVERSE SECTION. 



Hy. hyoid bone. Th. thyroid cartilage; On. cricoid cartilage; m.th.h. 

 thyro-hyoid membrane, all cut across. 



e. epiglottis, e' its cushion, c.v.s. ventricular bands, c.v. vocal cords, with v. 

 the ventricles of the larynx between them. T. the trachea. 



A. the internal thyro-arytenoid muscle, cut across ; it is seen to form the bulk 

 of the wedge-shaped projection of which the vocal cord is the extreme edge. B. 

 the external thyro-arytenoid, cut across. 



rhomboid, the obtuse angle on each side marking the attach- 

 ment of the vocal cord to the processus vocalis ; through this 

 wide opening the tracheal rings are clearly visible, and indeed 

 with an appropriate position of the mirror the bifurcation of the 

 trachea into the bronchi may under favourable circumstances be 

 observed. When changes in the voice or in the breathing are 

 being made, the white glistening vocal cords may be seen to 

 come together or to go apart like the blades of a pair of scissors. 



68 



