THE VOICE AND SPEECH. 439 



Anatomy of the Larynx. The principal parts entering into the 

 formation of the larynx (Figs. 302 and 303) are the thyroid cartilage; 

 the cricoid cartilage; the two arytenoid cartilages; and the two true vocal 

 oords (Fig. 307). The epiglottis (Fig. 303) has but little to do with the 

 voice, and is chiefly useful in protecting the upper part of the larynx 

 from the entrance o.f food and drink in deglutition. It also probably 

 guides mucus or other fluids in small amount from the mouth around 

 the sides of the upper opening of the glottis into the pharynx and ceso- 

 phagus, thus preventing them from entering the larynx. The false 

 vocal cords (cvs, Fig. 307), and the ventricle of the larynx, which is a 

 space between the false and the true cord of either side, need be here only 

 referred to. 



Cartilages. (a) The thyroid cartilage (Fig. 304, 1 to 4) does not 

 form a complete ring around the larynx, but only covers the front por- 

 tion, (b) The cricoid cartilage (Fig. 304, 5, 6), on the other hand, is a 

 complete ring; the back part of the ring being much broader than the 

 front. On the top of this broad portion of the cricoid are (c) the aryte- 

 noid cartilages (Fig. 304, 7), the connection between the cricoid below 

 and arytenoid cartilages above being a joint with synovial membrane and 

 ligaments, the latter permitting tolerably free motion between them. But 

 although the arytenoid cartilages can move on the cricoid, they of course 

 accompany the latter in all its movements, just as the head may nod or 

 turn on the top of the spinal column, but must accompany it in all its 

 movements as a whole. 



Joints and Ligaments. The thyroid cartilage is also connected 

 with the cricoid, not only by ligaments, but also by joints with synovial 

 membranes; the lower cornua of the thyroid clasping, or nipping, as it 

 were, the cricoid between them, but not so tightly but that the thyroid 

 can revolve, within a certain range, around an axis passing transversely 

 through the two joints at which the cricoid is clasped. The vocal cords 

 are attached (behind) to the front portion of the base of the arytenoid 

 cartilages, and (in front) to the re-entering angle at the back part of the 

 thyroid; it is evident, therefore, that all movements of either of these 

 cartilages must produce an effect on them of some kind or other. Inas- 

 much, too, as the arytenoid cartilages rest on the top of the back portion 

 of the cricoid cartilage, and are connected with it by capsular and other 

 ligaments, all movements of the cricoid cartilage must move the aryte- 

 noid cartilages, and also produce an effect on the vocal cords. 



Intrinsic Muscles. The so-called intrinsic muscles of the larynx, 

 or those which, in their action, have a direct action on the vocal cords, 

 are nine in number four pairs, and a single muscle; namely, two 

 crico-thyroid muscles, two thyro-arytenoid, two posterior crico-arytenoid, 

 two lateral crico-arytenoid and one arytenoid muscle. Their actions are 

 as follows: When the crico-thyroid muscles (10, Fig. 306) contract, they 

 rotate the cricoid on the thyroid cartilage in such a manner, that the 

 upper and back part of the former, and of necessity the arytenoid car- 

 tilages on top of it, are tipped backwards, while the thyroid is inclined 

 forward; and thus, of course, the vocal cords being attached in front to 

 one, and behind to the other, are " put on the stretch." 



The thyro-arytenoid muscles, on the other hand, have an opposite 

 action pulling the thyroid backwards, and the arytenoid and upper 

 back part of the cricoid cartilages forwards, and thus relaxing the vocal 

 cords. 



