114 AVES. 



fifth bronchial ring. Upon the internal side of the tympaniform 

 membrane, which is thrown into vibrations during the passage of the 

 air from the lungs, there is placed a strip of membrane, which also 

 vibrates and may be regarded as corresponding to the ligamentum 

 vocale externuin of the Singing-birds. 



The structure of the inferior larynx is still more complicated in 

 the Singing-birds, and those birds generally which are provided with 

 what is called a true muscular vocal apparatus, among these 

 the Ravens being included, from the power they possess, like the 

 Parrots, of imitating the human voice. Although a number of 

 slight varieties occur in the different genera and species, which 

 stand in direct relation with the degree of complexity of their song, 

 still, however, a great general conformity may be perceived in the 

 structure of the singing apparatus, it, as a rule, being formed of 

 five well-developed pairs of muscles. In the Nightingale and other 

 small Singing-birds, this muscular apparatus is indeed very power- 

 fully developed, but on account of its small size, the student will do 

 best to select a larger bird, as the Raven or Rook, for the purposes 

 of examination. 



The trachea here consists of a short bony tympanum or drum, 

 constituting its inferior extremity, and usually formed by the early 

 coalescence of three rings. The tympanum is divided as usual infe- 

 riorly by a transverse or cross bone. From the superior border of 

 this, a membranous semilunar fold (membrana semilunaris Savart) 

 rises to about a line in height, as in the Rook ; its dimensions, how- 

 ever, are very various, and in birds of accomplished song, or such 

 as can learn to speak, it is more largely developed. In other Pas- 

 seres, as in the Sparrow, Haw-grosbeak, &c., these membranes are 

 of course wanting. From these observations it may be inferred that 

 this membrane is of essential importance to the production of song 

 or the power of uttering articulate sounds, since when it is absent or 

 slightly developed, the voice is feeble or has but little variety of 

 tone. The first three bronchial demi-rings exhibit also remarkable 

 peculiarities. The first or uppermost ring is thicker in the middle 

 than at the extremities ; at the posterior end inferiorly it be- 

 comes broader, and curves in such a manner backward and in- 

 ward, as to form the posterior and internal wall of the bronchial 

 portion of the inferior larynx ; below it passes into an acute angle, 

 which forms the point of support of the internal lip of the glottis. 

 The second bronchial demi-ring is more moveable than the first, 

 especially in the direction outward and upward. The third demi- 



