316 Mr. Yarreut on the Organs of Voice in Birds. 
to the consideration of the most complex organ, that furnished 
with five pair. 
 'The birds included in this division are all the Corvi, Starling, 
Thrush tribe, Larks, Buntings, Finches, Warblers, Swallows, 
c., the organs of voice in which vary only in size. ‘The tube 
of the trachea is generally uniform:in shape throughout, the 
bronchie long in proportion, and both parts perfectly flexi- 
ble. Tas. XVIII. Fig. 9. 10. & 11. are an anterior, posterior, 
and side view of a portion of the trachea and its muscles in the 
Raven, which may be considered as the type of this form, and 
from its size admits of clear explanation. Tas. XVII. Fig. 9. is 
a side view of the same part divested of its muscles, to show by 
the prevalence and interposition of membrane the degree of 
alteration the various muscles are able to effect. 
Tas. XVII. Fig. 10. represents part of the same trachea, 
one bronchia hating been removed to show the membrana tym- 
paniformis, letter c, on the inner side of the other. Tas. XVII. 
Fig. 11. is a view of the under surface of the bone of divari- 
cation. Letter a with a cross is the wider posterior part to 
admit the passage of the esophagus from behind forwards, be- 
tween the bronchiz, when both are in their natural situation. 
Letters a, in d 11. & 12. mark the situation of the cross- 
bone. - oe | 
Referring npaii: a ichs XVII Figel bis: the pair of muscles 
which descend on the outside of the trachea, divide at a short - 
distance above the end of the tube, and send one portion in 
continuation downwards and backwards, to be inserted upon 
the extreme posterior end of the first bone of the bronchia, 
and is marked f. Its counterpart (e) passes from the place of 
separation downwards and forwards, to be inserted below the 
extreme point of the last bone of the tube. Within the angle 
formed by the separation of these two muscles, a third slender 
and 
