222 



ANATOMY OF VERTEBRATES. 



102 



Birds^ and, being vibratile, forms an important part of their trilling 

 vocal apparatus. The air passes on each side the membrana semi- 

 lunaris and its sustaining bone to and from the bronchi and lungs. 

 The walls of the loAver larynx are formed by modified rings and 

 half-rings of the end of the trachea and beginning of the bronchi. 

 The last ring of the trachea, fig. 103, t, 

 usually expands as it descends, with its fore 

 and hind 2:)arts produced, and the lower lateral 

 borders concave : the extremities of the pes- 

 sulus, fig. 102, ?, abut against the produced 

 angles, and expand to be there connected, 

 also, with the fore and hind terminations of 

 the first half- ring of the bronchus, fig. 103, 

 «, strengthening and clamping together the 

 upper parts of the vocal framework. The 

 second bronchial half-ring, ib. h, is flattened 

 and curved with the convexity outward, 

 like the first, but is more moveable. The 

 third half-ring, ib. c, is less curved and fur- 

 ther separated from the second, to the ex- 

 tremities of which its own are connected by 

 ligament, and, for the intervening extent, 

 by membrane ; its inner surface supports 

 the fibrous chord or fold which forms the outer lip of the glottis of 

 that side ; it is susceptible of a rotatory movement on its axis, and 

 is an important agent in the modulation of 

 the voice. All the above parts, t, «, h, c, 

 fig. 103, are bony. The bronchial half- 

 rings and their connecting ligaments and 

 membranes form the outer convex wall of 

 the tube : the inner wall is a flat membrane, 

 stretched like a drum-head, between the 

 extremities of the half-rings, and attached 

 above to the cross-bar, and through it to 

 the semilunar membrane. The outer part 

 of the lower tracheal and bronchial rings, 

 being cut away in fig. 102, exposes the 

 central surface of the 'membrana tympa- 

 niformis,' g^ with its upper connexions with 

 the cross-bone /, and the 'membrana semilunaris,' Ji. Part of 

 the peripheral surface of the tympaniform membrane is seen in 

 the front view of the lower larynx and bronchi, fig. 104, a, g. 

 A small appendage to the inner margin of the half-ring, fig. 



Side view of cavity of lower 

 larynx, Raven, yxx-. 



103 



Lower larynx, Raven, xxx'. 



