VOCAL OEGANS. 



729 



Fig. 361. 



Cartilages of the superior larynx of a bird. 



membranes of the trachea, and thus keep the air-passages constantly 

 permeable to the atmosphere. 



(2066.) In many birds, especially 

 among* the web-footed tribes, the 

 trachea suddenly dilates into wide 

 chambers or cavities of different 

 forms and dimensions a circum- 

 stance the object of which has not 

 as yet been satisfactorily explained ; 

 and, what is still more inexplicable, 

 in some genera, and those too with 

 the longest necks, as, for example, the 

 Wild Swan and many of the Wading 

 birds, the lower part of the trachea 

 is lengthened out and variously 

 contorted before it terminates in the 

 chest. This long trachea is provided 



with muscles whereby the rings may be approximated ; and thus the 

 length of the tube is considerably modified: these muscles (fig. 360, A, B,^,) 

 arise from the sternum, and sometimes also from the furcula, and are 

 continued along the sides of the windpipe throughout its whole length. 



(2067.) The upper larynx, or rima glottidis, is in Birds but of 

 secondary importance in the production of vocal sounds : it is a simple 

 fissure bounded by two osseous pieces (fig. 361, A, B, /), corresponding 

 with the arytenoid cartilages of Mammalia ; these, however, in the Bird 

 are not connected with chordae, vocales, but simply, as they are separated 

 or approximated, open or close the fissure of the glottis. When, there- 

 fore, we compare the framework of this organ with the cartilaginous 

 pieces found in the larynx of Mammalia, considerable difference is per- 

 ceptible, insomuch that it is not easy positively to recognize the analo- 

 gous portions, more especially as in the Bird the cartilages are more or 

 less completely ossified. If the broad anterior plate (fig. 361, 6) be 

 considered as the thyroid cartilage, we must suppose the cricoid to be 

 represented by three distinct ossicles, two of which (cc) are lateral, 

 while the third or central portion (e) supports the arytenoid bones (//), 

 which are moveably articulated with its anterior margin. The aryte- 

 noid bones themselves are of an elongated form, and each presents a 

 long process (g g) for the insertion of the muscles that act upon them. 

 These arytenoid bones are moved by two pairs of muscles the super- 

 ficial pair (fhyro-arytenoidei) (fig. 362, B) serving to pull asunder, while 

 the more deeply-seated (constrictores glottidis) (fig. 362, A) bring toge- 

 ther the lips of the glottis. 



(2068.) It is the lower larynx, situated at the opposite extremity of 

 the trachea, at the point where that tube gives off the bronchi, that the 

 real vocal apparatus of birds is situated ; and in the more perfect Singing 



