926 



OF THE VOICE AND SPEECH. 



Thyroid cartilage just 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 a 



Fig. 232. 



Fig. 233. 



Bird's-eye view of Larynx from above : G E H, 

 the thyroid cartilage, embracing the ring of the 

 cricoid r u X to, and turning upon the axis x z, 

 which passes through the lower horns, c, Fig. 

 231. N F, N F, the arytenoid cartilages, connected 

 by the arytenoideus transversus. T v, T v, the 

 vocal ligaments. N x, the right crico-arytenoideus 

 lateralis (the left being removed). V k f, the left 

 thyro-arytenoideus (the right being removed). 

 H Z, N I, the crico-arytenoidei postici ; B, u, the 

 crico-arytenoid ligaments. 



Posterior view of larynx, and part of tra- 

 chea, dissected to show the muscles, a. Right 

 arytenoid cartilage, t, t. Posterior margins 

 of thyroid cartilage, c. Back of cricoid car- 

 tilage, h. Oshyoides. e. Epiglottis, b. Left 

 posterior crico-arytenoid muscle, s. Arytenoid 

 muscle. I. Fibrous membrane at back of tra- 

 chea, with the glands lying in it. n. Muscular 

 fibres of the trachea, r. Cartilaginous rings 

 of trachea. 



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. 



929. The depression of the front of the thyroid cartilage, and the consequent 

 tension of the vocal Ligaments, is occasioned by the conjoint action of the 

 Crico-thyroidei on both sides j and the chief antagonists to these are the Thyro- 

 arytenoidei, 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 men- 

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

 of the Crico-arytenoidei postici of the two sides, which proceed from their outer 

 corners, and turned somewhat round the edge of the Cricoid, to be attached to 



