212 HLEMETTTS OP OENITHOLOGX. 



of the bronchi which look towards each other are at their upper 

 part merely membranous, forming what is called the memhrana 

 tympaniformis (figs. 163 & 164, jr). The coalesced rings of the 

 lower part of the trachea form a chamber called the tympanum of 

 the trachea. Internally, the syrinx is generally divided by a bar 

 of bone, the os transversale or pessulus, from the upper margin of 

 which a delicate membrane ascends into the cavity of the tym- 

 panum of the trachea, ending in a free concave margin, whence 



Pig. 163. 



Side View of Cavity op Larynx op Eaven. 



The outer part of the lower end of the ti-aehea and of the bronchus next 

 the spectator being cut away to show the interior. 



i, Os transversale, pessulus, or bony bar traversing the lower end of the 

 trachea from before backwards, and having an opening into one of the 

 bronchi on either side of it ; h, memhrana semilunaris ascending from 

 the 03 transversale, and terminating within the trachea by a free con- 

 cave margin ; g, membranous inner wall of the bronchus or membrana 

 tympaniformis connecting the inner extremities of the bronchial half- 

 rings. 



it is termed the memhrana semilunaris. This highly elastic mem- 

 brane, together with two other elastic folds of membrane, which 

 project inwards from the outer side of the commencement of 



