THE GLOTTIS AND THE LARYNGEAL POUCH. 693 



Action. This muscle draws downwards the epiglottis and aryteno- use. 

 epiglottidean fold, and assists in closing the upper aperture of the 

 larynx. 



CAVITY OF THE LARYNX AND FARTS INSIDE. On looking into the interior of 

 cavity of the larynx from above, the tube will be seen to become Se cavity is 

 narrower from above downwards, owing to the projection inwards of constricted 

 two prominent folds on each side termed the vocal 'cords. The lower 

 or true vocal cords are placed on a level with the bases of the ary- 

 tenoid cartilages, and the slit-like interval between them is called 

 the glottis. Below this the cavity enlarges again to the lower 

 i'ip>rrtnre of the larynx, where it is continued into the trachea. 



Upper aperture of the larynx (fig. 233, N, p. 659). This is the orifice Upper open- 

 by which the larynx communicates with the pharynx. It is tri- mg: 

 angular in shape, with the base, which is formed by the epiglottis, form and 

 turned forwards and upwards. The sides, which are sloped from. c 

 before downwards and backwards, are formed by the aryteno-epi- 

 glottidean folds of the mucous membrane ; and at the apex is the 

 arytenoid muscle, with the upper ends of the arytenoid cartilages, 

 covered by the mucous membrane. This aperture is closed by the 

 tubercle of the epiglottis during deglutition. 



The lower aperture of the larynx, bounded by the lower edge of Lower open- 

 the cricoid cartilage, is nearly circular in form, and of the same size m 

 as the interior of the cartilage. 



Dissection. To see the parts within the larynx, the tube is to be Dissection, 

 divided by a median incision along the back ; but in cutting through 

 the arytenoid muscle, let the knife be carried a little to the right of 

 if middle line, so as to avoid the nerves entering it. 



On the side wall of the larynx (fig. 247, p. 695) there will now be Parts inside 

 seen the projecting bands of the vocal cords separated by a depression arynx * 

 called the ventricle of the larynx (A). If a probe be passed into this 

 hollow, it will enter a small pouch sacculus laryngis (D), by an 

 aperture at the upper and fore part, under cover of the superior 

 vocal cord. 



The glottis or rima glottidis is the narrowest part of the laryngeal Glottis : 

 cavity, and is placed on a level with the bases of the arytenoid position, 

 cartilages. If the cut surfaces of the back of the larynx be placed forms and 

 together, it will be seen to have the form of an elongated triangle, boundaries ; 

 with the base turned backwards. It is bounded on the sides by 

 the true vocal cords (B) in the anterior two-thirds of its extent, 

 and by the arytenoid cartilages (E) in the posterior third. In front, 

 the right and left vocal cords meet at their attachment to the 

 thyroid cartilage ; and behind, the base is formed by the arytenoid 

 muscle. The portion of the slit between the vocal cords, being subdivision, 

 alone concerned in the production of the voice, is distinguished as 

 the vocal glottis, while the part between the arytenoid cartilages is 

 termed the respiratory glottis. 



The size of the glottis differs in the two sexes ; and its form Size and 

 undergoes frequent changes during life, caused by the movements of 

 the arytenoid cartilages and the vocal cords. In the male, the length, 



