STKUOTTJEK OF THE LABYNX 487 



top of the trachea or windpipe. This box is prominent 

 externally as a projection which we call the Adam's apple. 



Structure of the larynx. — The larynx or voice box is 

 composed of cartilages, membranes, and muscles. The 

 front and sides are formed of a single large cartilage (the 

 thyroid). The curved front of this cartilage has a pro- 

 jection at the top like the lip of a pitcher (the Adam's 

 apple). It curves around on each side in broad, flat 

 sheets, which end above and below as projecting points. 

 The two upper points are attached by ligaments to the 

 hyoid bone and the two lower projections fit into sockets 

 in a second cartilage called the cricoid. 



This cricoid cartilage is a complete ring. The broad 

 part of this ring forms the back of the larynx, while the 

 narrow part encircles the front of the box just below the 

 thyroid. On the top of the broad part of the cricoid are 

 two triangular cartilages (the arytenoids) whose bases 

 form true joints with the cricoid and whose apices extend 

 upward. By means of the joints all these cartilages can 

 move freely upon one another. Beside these four hyaline 

 cartilages there are five yellow cartilage structures. One, 

 the epiglottis, is attached to the top and front of the 

 thyroid, and projects upward to form a lid for the box. 

 Two others form small horn-shaped projections on the top 

 of the ar5rtenoids and the remaining two are inclosed in 

 folds of the membranous lining of the box. 



The box is lined with a smooth layer of mucous mem- 

 brane. This layer is smooth, except at the point where the 

 glottis or pharynx opening is located. Here it is thrown 

 outward in two sets of ridges. The upper ridges are called 

 the false vocal cords. They have nothing to do with voice 

 production, but help to close the glottis. The two lower 



