174 HAND-BOOK OF PHYSIOLOGY. 



side, except by means of the respiratory passages. The air enters these 

 passages through the nostrils or through the mouth, thence it passes 

 through the larynx into the trachea or windpipe, which about the middle 

 of the chest divides into two tubes, bronchi, one to each (right and left) 

 lung. 



The Larynx is the upper part of the passage which ieaas exclusively 

 "to the lung; it is formed by the thyroid, cricoid, and arytenoid cartilages 

 (Fig. 145), and contains the vocal cords, by the vibration of which the 

 voice is chiefly produced. These vocal cords are ligamentous bands at- 

 tached to certain cartilages capable of movement by muscles. By their 

 approximation the cords can entirely close the entrance into the larynx; 

 lout under the ordinary conditions, the entrance of the larynx is formed 

 by a more or less triangular chink between them, called the rima glot- 

 tidis. Projecting at an acute angle between the base of the tongue and 

 the larynx to which it is attached, is a leaf-shaped cartilage, with its 

 larger extremity free, called the epiglottis (Fig. 145, e). The whole of the 

 larynx is lined by mucous membrane, which, however, is extremely thin 

 over the cords. At its lower extremity the larynx joins the trachea. 1 

 With the exception of the epiglottis and the so-called cornicula laryngis, 

 the cartilages of the larynx are of the hyaline variety! 



Structure of Epiglottis. The supporting cartilage is composed of 

 yellow elastic cartilage, enclosed in a fibrous sheath (perichondrium), 

 and covered on both sides with mucous membrane. The anterior surface, 

 which looks toward the base of the tongue, is covered with mucous mem- 

 iDrane, the basis of which is fibrous tissue, elevated toward both surfaces in 

 the form of rudimentary papillae, and covered with several layers of 

 squamous epithelium. In it ramify capillary blood-vesse.ls, and in its 

 meshes are a large number of lymphatic channels. Under the mucous 

 membrane, in the less dense fibrous tissue of which it is composed, are a 

 number of tubular glands. The posterior or laryngeal surface of the 

 epiglottis is covered by a mucous membrane, similar in structure to that 

 on the other surface, but that the epithelial coat is thinner, the number 

 of strata of cells being less, and the papillse few and less distinct. The 

 fibrous tissue which constitutes the mucous membrane is in great part of 

 the adenoid variety, and this is here and there collected into distinct masses 

 or follicles. The glands of the posterior surface are smaller but more 

 numerous than those on the other surface. In many places the glands 

 which are situated nearest to the perichondrium are directly continuous 

 through apertures in the cartilage with those on the other side, and often 

 the ducts of the glands from one side of the cartilage pass through and 

 open on the mucous surface of the other side. Taste goblets have been 



1 A detailed account of the structure and function of the Larynx will be found in 

 Chapter XVI. 



