SYRINX. 



443 



The lower larynx or syrinx. Except in the ostrich, storks, 

 and some vultures, the vocal organ is placed lower down on the 

 trachea usually at the point where the trachea divides into the 

 bronchi, so that both divisions take part in its formation (Fig. 

 244). The last tracheal rings and the anterior bronchial rings 

 have a modified form, and are often intimately cormected with 

 each other ; the end of the trachea and the beginning of the 

 bronchi are compressed or dilated into a vesicular form and 

 transformed into the so-called tympanum, which in the males of 

 many ducks is dilated into unsymmetrical secondary cavities 

 (tympanic cavity and labyrinth), which serve as a resonating 

 apparatus. The part of the trachea from which the bronchi 



FIG 24T.-l.o\ver larvnx of raven (from Owen), a side view of larynx laid open ; 6 larynx 

 after removal of muscles ; c larynx with muscles from the front ; d froin the side M 



muscles: Ms membrana semilunaris; Mty membrana tympaniformis interna , Rb the 

 modified three first bronchial rings ; Rt modified last tracheal rmg ; St pessulus. 



pass off (i.e. tympanum) is traversed in a horizontal direction 

 by a projecting osseous band— the pessulus— which forms a ver- 

 tical septum between the anterior apertures of the two bronchi. 

 This septum, at its anterior (ventral) and posterior (dorsal) ends, 

 gives off on each side two arched processes, which pass down- 

 wards—one along the dorsal, and the other along the ventral 

 edge of the bronchus of its side ; and between these comua the 

 internal wall of each bronchus, which is here membranous, is 

 stretched, and constitutes the membrana tympaniformis interna. 

 In the singing bkds {Oscines) there is, m addition, a semi-lunar 

 fold {membrana semilunaris) on the pessulus as a prolongation 



