344 CLASS xvi. 



the consideration of the vocal organs. The wind-pipe of birds dif- 

 fers from that of other vertebrate animals that breathe by means of 

 lungs in regard to the part it takes in the production of the voice. 

 In the mammals, and also in the reptiles, the trachea merely con- 

 ducts the air which is to serve for the production of sound; in 

 birds, on the contrary, it conducts the voice itself, which is not pro- 

 duced at the upper end of the wind-pipe, in the larynx, but at its 

 inferior extremity, where it divides into the two bronchi. Here 

 there exists an apparatus which has been improperly named inferior 

 larynx 1 . Seldom only is the organ for the production of sound 

 situated at the lower part of the trachea itself, above its division 

 into the bronchi, as in Tamnophilus and Myiothera; in Steatornis, 

 conversely, MUELLER found that the inferior larynx is seated in 

 each of the bronchi at some distance below the division, and thus is 

 double 2 . In most birds the rings of the bronchi are incomplete; 

 and on the inner surface, where they are turned towards each other, 

 there is a membrane which is tense and capable of vibration. 

 From the origin of the bronchi there ordinarily passes a bony 

 lamina transversely from before backward and extending upwards 

 into the trachea, along which a production of that membrane 

 mounts on each side, and is often continued into a border at its free 

 upper margin (membrana semilunaris) . In the parrots this partition 

 is wanting. On the outside of each of the bronchi is a fold of the 

 mucous membrane projecting inwards, provided with elastic fibrous 

 tissue, and forming a vibrating vocal ligament (lamina glottidis). 

 Very various are the muscles which move this apparatus. In very 

 many birds (gallinaceous birds, ducks, &c.) the lower larynx has 

 no proper muscles, but the vocal ligaments are slackened by 

 muscles which draw downwards and shorten the wind-pipe. A 

 pair of these muscles (musculi sterno-tracheales) is the only part of 

 the motor system of the wind-pipe that is constantly present. 

 These muscles ascend from the inner surface of the superior angles 

 of the sternum along the wind-pipe, and are inserted into it at a 

 greater or less height. A second pair of muscles, less constant 

 than the preceding, ascends from the furcular clavicle to the wind- 



1 This is wanting in only a few birds, as the stork, the struthious birds and the 

 genus Cafhartes ILLIG. 



2 Archiv, 184?, s. 7, Tab. I. fig. ult. 



