BIRDS. 345 



pipe. In addition to these most birds have some proper muscles of 

 the inferior larynx which draw one or more rings (the second and 

 third) of the bronchi upwards, running from the lower part of the 

 trachea to these rings or to the membranous space on the outside of 

 the base of the bronchi. In many songsters of the old world five 

 or six pairs of these muscles have been distinguished; and hence 

 this complex system of muscles (for singing) has been incorrectly 

 ascribed to all the Passerines, which however in very many Ame- 

 rican, especially South- American genera, is not present 1 . The 

 sound produced in the inferior larynx is conducted, and also in 

 some degree modified, by the wind-pipe and the superior larynx. 

 The wind-pipe of birds consists of perfectly closed cartilaginous, or 

 in very many genera bony rings, which are connected by membra- 

 nous, mostly small, interspaces. It is, in accordance with the neck, 

 of remarkable length, and forms in some waders, swimmers and 

 a few gallinaceous birds special curvatures, mostly included in the 

 sternum, principally (or sometimes solely) in male individuals, yet 

 also equally developed in both sexes, as in the wild swan (Anas 

 cygnus L. or Cygnus musicus}. In some male birds the wind-pipe 

 has nearly mid-way an oval flat expansion (Anas clangula, Anas 

 fusca, &c.); sometimes two such expansions lie one behind the 

 other (Mergus merganser) 2 . Birds, whose voice has a very exten- 

 sive musical scale, are able to shorten and lengthen their wind-pipe 

 considerably, and, to that end, have very thin rings and larger mem- 

 branous interspaces. The inferior rings of the wind-pipe above the 

 bronchi are usually nearer together, or are connected by longitudinal 

 processes, or even, as in many songsters, have wholly coalesced to 

 form a continuous bony cylinder. We may also remark, that in 



1 Compare CUVIER Magasin encyclopedique, Tome n. No. 7, p. 330, suiv., and 

 translated (uber den untern Larynx der Vogel) in REIL'S Archiv, v. s. 67 91, and 

 Lecons d'Anat. comp. iv. pp. 450491, sec. e"dit. vin. 730 772; SAVART Memoire 

 sur la voix des Oiseaux, Ann. de Ckemie et de Physique, 1826, MaietJuin; and J. 

 MUELLER Ueber die bisher unbeJcannten typischen Verschiedenheiten der Stimm- Organe 

 der Passerinen, Abhandlungen der Alcad. d. Wissensch. zu Berlin, Physik. Mathem. 

 Klasse, 1845, s. 321 391, Tab. I. vi. 



2 Compare YARRELL Observations on the Tracheae of Birds, Linn. Transact, xv. 

 1827, pp. 378 391, with many figures. In no bird perhaps is the trachea compara- 

 tively longer than in Anas semipalmata LATH., where it makes four curvatures before 

 dividing into the bronchi; see PI. 13. 



