316 Mr. Yarrell 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 

 bronchiae long in proportion, and both parts perfectly flexi- 

 ble. Tab. 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. Tab. 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. 



Tab. XVII. Fig. 10. represents part of the same trachea, 

 one bronchia having been removed to show the membrana tym- 

 paniformis, letter c, on the inner side of the other. Tab. 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 oesophagus from behind forwards, be- 

 tween the bronchiae, when both are in their natural situation. 

 Letters a, in Fig. 11. & 12. mark the situation of the cross- 

 bone. 



Referring again to Tab. XVIII. Fig. 11. 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 



