124 



THE BIOLOGY OF BIRDS 



of the windpipe. The cartilages of the larynx are biologi- 

 cally interesting, for they are the transformed representatives 

 of branchial arches — an instance of a common method of 



organic evolution, mak- 

 ing a new thing out of an 

 older thing. The larynx 

 and the vocal cords began 

 in Amphibians. 



The trachea is sup- 

 ported by bony " rings," 

 usually, but not always, 

 complete. In mammals 

 the rings are gristly. 

 The trachea is sometimes 

 much longer than the 

 neck ; it is coiled inside 

 the breastbone in the 

 Whooper Swan, outside 

 the breastbone in the 

 Capercailzie. It is moved 

 by two sterno-tracheal 

 muscles attached to the 

 front of the breast-bone. 

 The syrinx or song- 

 box at the base of the 

 trachea is absent in os- 

 triches, storks, and some 



—Part of breathing system of a vulturCS. It is an en- 



From a specimen, i , the tongue ; i „. r .1 u„„„ ^f 



2, the glottis or entrance to windpipe; I'^lfgement of the base of 



3, the voiceless larynx; 4, posterior the trachea and of the 

 " iiorns " of the hvoid, to which some r-^. . „^ ^^ +1,^^^ ,-,*^rTo r^f 

 tongue muscles are attached; 5, the ^rst tWO or three nngS ot 

 windpipe; 6, the syrinx or song-box; the bronchial tubes, and 



8* o^^^he kings'' """'''"^ '^' '^'""'' ' ^^ contains the stretched 



vocal cords which vibrate 

 more or less musically when the expired air passes rapidly 

 over them. There is a somewhat complex skeleton and 

 musculature. There may be an asymmetrical accessory 

 chamber or labyrinth in addition to the main cavity or 



Ftr;. 30 

 bird. 



