LARYNX AND PHONATION. 349 



find the clastic tissue which we have already observed along 

 the trachea, formed, as always, of fibres irregularly inter- 

 laced and twisted like horse-hair in a mattress ; at the glottis 

 this tissue forms a thicker layer, which has been considered 

 in anatomy as a ligament, subjacent to the mucous layer; this 

 is what is called the vocal cord. 



Below this elastic tissue is also found the muscular layer, 

 as is the case throughout the respiratory tree ; in the larynx, 

 however, we find the striated and not the smooth muscle : 

 it forms here, as in all the organs of animal life (vie de 

 relation), clearly defined muscular bodies, and with functions 

 well determined (posterior crico-arytenoid muscles, lateral 

 crico-arytenoid muscles, ary-arytenoid, and thyro-arytenoid 

 muscles), (Fig. 85). Finally, the cartilaginous rings of the 

 trachea are also arranged for the purpose of forming special 

 and characteristic pieces or parts (thyroid, cricoid, and ary- 

 tenoid cartilages), (Figs. 87 and 88). 



Aperture of the Glottis. The inferior laryngeal constric- 

 tion, or glottis, properly so-called, exhibits, when examined 

 from above, the form of a triangular slit, like the head of a 

 spear, the upper part being in 

 front, and the base behind : this 

 base is formed by the ary-aryte- 

 noid muscles. The sides of the 

 triangle are composed in its an- , rap 

 terior three-fifths by the vocal 

 cords, in the posterior two-fifths 

 by the edges of the arytenoid 

 cartilages (Figs. 86, 87, 88, 89, 



90). These Cartilages form tri- Fig. 86. -Aperture of the glottis, seen 



angular pyramids : their base is in the living body by means of the 



f . (. . , IP laryngoscope.* 



a triangle, one of the angles of 



which is anterior, another posterior, and the third external ; 

 one of the sides of this triangle is thus internal, and forms 

 the posterior part of the glottis. Each arytenoid cartilage, 

 at its articulation with what is called the articular facet of 

 the cricoid (see Figs. 87 and 88, and farther on, Figs. 90 and 

 91), can turn on its vertical axis, in such a manner that its 

 anterior angle (or vocal process) is turned either inwards 

 or outwards, thus necessarily modifying the whole form of 

 the rima glottidis (or glottid chink), since this angle is the 



* or, Aperture of the glottis, ri, Lower vocal cords, rs, Upper vocal cords 

 fir, Arytenoid cartilage, rap. Aryteno-epiglottidean folds, b. Cushion oil the 

 epiglottis. (L. Maud'].) 



