846 



OF THE VOICE AND SPEECH. 



dered more or less tense, by the movement of the Thyroid cartilage thus 

 described ; being tightened by the depression of its front upon the Cricoid 

 cartilage, and slackened by its elevation. On the other hand, they may be 

 brought into more or less close apposition, by the movement of the Arytenoid 

 cartilages; being made to approximate nearly, or to recede in such manner 

 as to cause the rima glottidis to assume the form of a narrow V, by the 

 revolution of these cartilages. We shall now inquire into the actions of the 

 muscles upon the several parts of this apparatus; and first into those of the 

 larynx alone. 



692. The depression of the front of the Thyroid cartilage, and the conse- 

 quent tension of the Vocal Ligaments, is occasioned by the conjoint action 

 of the Crico-thyroidei 1 (Fig. 299, A K) on both sides; and the chief antago- 

 nists to these are the Thyro-arytenoidei (Fig. 298, F m, Fig. 300, v &/), which 

 draw the front of the thyroid back towards the arytenoid cartilages, and thus 

 relax the vocal ligaments. These two pairs of muscles may be regarded as 

 the principal governors of the pitch of the notes, which, as we shall hereafter 

 see, is almost entirely regulated by the tension of the ligaments ; their action 

 is assisted, however, by that of other muscles presently to be mentioned. 2 - 

 The arytenoid cartilages are made to diverge from each other, by means 

 of the Crico-arytenoidei postici (Fig. 300, N I) of the two sides, which 



proceed from their outer corners, 

 and turn somewhat round the edge 

 of the Cricoid, to be attached to the 

 lower part of its back ; their action 

 is to draw the outer corners back- 

 wards and downwards, so that the 

 points to which the vocal ligaments 

 are attached are separated from one 

 another and the rima glottidis is 

 thrown open. This will be at once 

 seen from the succeeding diagram, 

 in which the direction of traction of 

 the several muscles is laid down. 

 The action of these muscles is partly 

 antagonized by that of the Crico- 

 arytenoidei laterales (Fig. 300, NX), 

 which run forwards and downwards 

 from the outer corners of the Aryt- 

 enoid cartilages, and whose con- 



FIG. 300. 



traction tends to bring their anterior 

 points into the same straight line, 



Bird's-eye view of Larynx from above: o K H, the 

 thyroid cartilage, embracing the ring of the cricnid, 

 r u x w, and turning upon the axis, x z, which puss >s 

 through the lower horns, c, Fig. 298; N F, N K, the - 



arytenoid cartilages, connected by the arytenoideus depressing them at the Same time, 

 transversus; T V, T v, the vocal ligaments; N x, the S RS tllUS to dose the glottis. These 

 ri,,h, crieo.arytenoH.eus ,ateralis (the ^ left bei,,, re- mus( , ]es are assist ed by the A H,t- 

 moved); v k /, the lett thyro-arytenoideua (the right . , _, /rw_ OAA^ 



being removed) ; N /, N /, the crico-arytenoidei postici ! 

 ii, it, the crico-arytenoid ligaments. 



enoideus transversus (Fig. 300), 

 which connects the posterior faces 



1 For a careful investigation in regard to the precise mode in which the crico- 

 thyroid acts, see .Jelentt'y, Pfliiger's Archiv, 1873, vol. vii, p. 8fi. 



1 Dr. P. Martyn has adduced various observations to show that the Thyroid body 

 exerts an important influence on the pitch of the notes, by giving a certain lirmness, 

 rigidity, and tension to the larynx. He also suggests that this body may act as a 

 lntnli-1-, rendering the vibrations of the vocal cords slower and longer, and tin; tone in 

 consequence, fuller, louder, and deeper, thus compensating for the small size of the 

 larynx; finally he believes that it aids, by its changes in shape, bulk, and density, in 

 producing the wonderful qualities of modulation and expression peculiar to the human 

 voice. See Proceedings of the Royal Society, vol. viii, p. 315. 



