RESPIRATORY ORGANS. 



29 



Inside the larynx are the vocal cords. These are folds of 

 the inner lining which stretch in pairs between the thyroid and 

 the arytenoids, and, by the motion of these cartilages, can be 

 tightened or relaxed. The upper pair of these are the false vocal 

 cords, so called since they play no part in the production of the 

 voice. The second or lower pair are the vocal cords proper. 

 Between the two is a depression, the ventricle of the larynx, or 

 sinus of Morgagni, which in certain apes becomes greatly devel- 

 oped as a vocal sac or resonator. In many anura the floor of the 

 mouth is capable of distention, and here serves as a resonator. 



Fig. 31. Diagram of the relationships of the 

 visceral arches in man, alter Wiedersheim. a, aryte- 

 noid ; bh, basihyal ; c, cricoid ; h, hyoid arch ; i, incus; 

 m, malleus ; mc, Meckel's cartilage ; y, stapes ; sf, 

 styloid process ; t, thyroid cartilage ; I-III branchial 

 cartilages. 



Fig. 32. Syrinx of 

 Sieatornis, after 

 Stejneger. 



In the mammals the anterior part of the larynx becomes 

 closely connected with the hyoid arch (see skeleton). 



In the birds, as was said above, the larynx tends to become 

 rudimentary. Its place as a vocal organ is taken by a ' lower 

 larynx,' the syrinx,^ developed at the lower end of the trachea, 

 or at the upper end of the bronchi where these arise from the 



1 Rudimentary in ostriches and some buzzards. 



