OP THE LARYNX, AND ITS ACTIONS. 

 Fig. 231. 



925 



External and Sectional views of the Larynx: A n B, the cricoid cartilage; E c a, the thyroid cartilage; a, 

 its upper horn ; c, its lower horn, where it is articulated with the cricoid; F, the arytenoid cartilage; E, F, the 

 vocal ligament ; AK, crico-thyroideus muscle ; F e m, thyro-arytenoideus muscle; x e, cricc-arytenoideus lateralis ; 

 s, transverse section of arytenoideus transversus; m n, space between thyroid and cricoid; B i, projection of 

 axis of articulation of arytenoid with thyroid. 



928. It will be remembered that the Trachea is surmounted by a stout car- 

 tilaginous annulus, termed the Cricoid cartilage ; which serves as a foundation 

 for the superjacent mechanism. This is embraced (as it were) by the Thyroid, 

 which is articulated to its sides by its lower horns, round the extremities of 

 which it may be regarded as turning, as on a pivot. In this manner the lower 

 front border of the thyroid cartilage, which is ordinarily separated by a small 

 interval from the upper margin of the cricoid, may be made to approach it or 

 recede from it ; as any one may easily ascertain by placing his finger against the 

 little depression which may be readily felt externally, and observing its changes 

 of size, whilst a range of different tones is sounded j for it will then be noticed that 

 the higher the note the more the two cartilages are made to approximate, whilst 

 they separate in proportion to the depth of the tones. 1 Upon the upper surface 

 of the back of the cricoid, are seated the two small Arytenoid cartilages ; these 

 are fixed in one direction by a bundle of strong ligaments, which tie them to 

 the back of the cricoid; but they have some power of moving in other directions, 

 upon a kind of articulating surface. The direction of the surface, and the mode 

 in which these cartilages are otherwise attached, cause their movement to be a 

 sort of rotation in a plane which is nearly horizontal but partly downwards ; so 

 that their vertical planes may be made to separate from each other, and at the 

 same time to assume a slanting position. This change of place will be better 

 understood, when the action of the muscles is described. To the summit of the 

 arytenoid cartilages are attached the chordae vocales or Vocal Ligaments, which 

 stretch across to the front of the thyroid cartilage ; and it is upon the condition 

 and relative situation of these ligaments that their action depends. It is evi- 

 dent that they may be rendered more or less tense, by the movement of the 



1 In making this observation, it is necessary to put out of view the general movement 

 to the larynx itself, which the finger must be made to follow up and down. 



