ORGANS OF VOICE AND RESPIRATION. 115 



ring is nearly straight, and between it and the second demi-ring 

 there is a triangular membranous fenestra, arid between the first 

 and second bronchial demi-ring an oval membrana tympaniformis 

 externa. Upon its inner surface there is found a remarkable fold 

 of the mucous membrane, consisting of tolerably thick and elastic 

 tissue ; it forms a true vocal chord, ligamentum vocale externum, 

 which always forms the external lip or wall of the glottidean fissure. 

 This membrane or fold is thrown into vibrations during the passage 

 of the air from the lungs. Besides this the membrana tympani- 

 formis internet is found as usual completing the inner side of the 

 bronchi, and is in continuous connexion with the membrana semi- 

 lunaris of the cross-bone. A small pliant cartilage (cartilago ary- 

 t&noidca Savart) is situated in the upper part of this membrane, is 

 in connexion with the second arch of bone, and exhibits manifold 

 diversities. 



Two anterior and three posterior pairs of muscles may be distin- 

 guished as belonging to the inferior larynx. In front, a long elevator 

 muscle (m. levator anterior longus) arises tolerably high up from 

 the trachea, and is firmly attached to the second bronchial demi-ring, 

 the anterior extremity of which it draws upward and outward, and so 

 widens the larynx. In like manner the transverse elevator (m. le- 

 vator anterior transversus) arises in front, but obliquely, from the ex- 

 ternal part of the superior border of the tympanum ; it proceeds in 

 the direction forward, and is attached by its inferior extremity to the 

 anterior part of the second and third bronchial demi-rings, and to 

 their interjacent membrane ; elevating and drawing these parts also 

 in the direction outward. By both- of these muscles, as well as by 

 the m. depressor trachea s. sterno-trachealis, which arises externally 

 from the tympanum and passes forward to the border of the sternum, 

 the tavity of the inferior larynx is shortened and dilated. The 

 membrana semilunaris and the ligamentum vocale externum will be 

 also synchronously stretched in a variety of ways by the action of 

 these muscles, joined to that of the three posterior pairs, the descrip- 

 tion of which will now occupy our attention. The posterior long 

 elevator (m. levator posterior longus) arises high up behind the 

 corresponding anterior elevator muscle, and is inserted posteriorly 

 into the extremities of the second bronchial demi-ring which it draws 

 upward, and at the same time rotates the third. The posterior 

 short elevator (m. levator posterior) is partly covered by the former 

 muscle, but is situated more in the direction backward and inward, 

 and at its origin from the upper part of the tympanum abuts closely 



