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HAND-BOOK OF PHYSIOLOGY. 



and excites contraction of the muscles that close the glottis. Both these 

 branches of pneumogastric co-operate also in the production and regula- 

 tion of the voice; the inferior laryngeal determining the contraction of 

 the muscles that vary the tension of the vocal cords, and the superior 

 laryngeal conveying to the mind the sensation of the state of these 

 muscles necessary for their continuous guidance. And both the branches 

 co-operate in the actions of the larynx in the ordinary slight dilatation 

 and contraction of the glottis in the acts of expiration and inspiration, 

 and more evidently in those of coughing and other forcible respiratory 

 movements. 



FIG. 298. Three laryngoscopic views of the superior aperture of the larynx aud surrounding- 

 parts. A, the glottis during the emission of a high note in singing; B, in easy and quiet inhalation of 

 air; C, in the state of widest possible dilatation, as in inhaling a very deep breath. The diagrams 

 A', B', and C', have been added to Czermak's figures, to show in horizontal sections of the glottis the 

 position of the vocal ligaments and arytenoid cartilages in the three several states represented in the 

 other figures. In all the figures, so far as marked, the letters indicate the parts as follows, viz. : I, 

 the base of the tongue; e, the upper free part of the epiglottis; e', the tubercle or cushion of the epi- 

 glottis; ph, part of the anterior wall of the pharynx behind the larynx; in the margin of the aryteno- 

 epiglottidean fold w, the swelling of the membrane caused by the cartilages of Wrisberg; s, that 

 of the cartilages of Santorini; a, the tip or summit of the arytenoid cartilages; c v, the true vocal 

 cords or lips of the rima glottidis; cvs. the superior or false vocal cords; between them the ventricle 

 of the larynx; in C, tris placed on the anterior wall of the receding trachea, and 6 indicates the com- 

 mencement of the two bronchi beyond the bifurcation which may be brought into view in this state 

 of extreme dilatation. (Czermak.) (From Quain's Anatomy.) 



Movements of Vocal Cords. The placing of the vocal cords in a 

 position parallel one with the other, is effected by a combined action of the 

 various little muscles which act on them the thyro-arytenoidei having, 

 without much reason, the credit of taking the largest share in the pro- 

 duction of this effect. Fig. 298 is intended to show the various positions- 



