272 ELEMENTS OF ORNITHOLOGY, 
of the bronchi which look towards each other are at their upper 
part merely membranous, forming what is called the membrana 
tympaniformis (figs. 163 & 164,q9). 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 
Fig. 165, 

Sipz View or Cavity or Larynx or Raven. 
The outer part of the lower end of the trachea and of the bronchus next 
the spectator being cut away to show the interior. 
7, 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 ; 4, membrana semilunaris ascending from 
the os transversale, and ter minating 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 membrana 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 
