314 Mr. Y ARRELL on the Organs of Voice in Birds. 
wil be found uniform in situation and shape throughout the 
whole of the Parrot tribe. The upper orifice is governed by two 
pair of muscles as in other birds ; and when mentioning the true 
muscles of voice, I refer only to those situated near the inferior 
larynx. As the organ of voice is more complex in these birds 
than in any of those hitherto noticed, it will be necessary to 
enter somewhat more into detail. The bony rings forming the 
tube of the trachea are strong, and of large size at the upper part, 
diminishing gradually as they approach the point of divarication, 
which is formed by the lower rings becoming elongated from 
before backwards, and terminating both before and behind in a 
small triangular-shaped bone (Tas. XVII. Fig. 8, 6) having its 
apex pointing downwards. To each side of the bottom of the 
tube there is attached by intervening membrane a thin crescent- 
shaped bone (TaB. XVII. Fig. 6, 2), the horns of which, directed 
also downward, pass below the points of the triangular interposed 
bones ; the connecting membrane permitting a certain degree of 
lateral motion in the inferior edges of both these crescent-shaped 
portions of bone. ‘Tas. XVII. Fig. 6. 7. & 8, represent these 
parts as they appear when divested of their muscles in the great 
blue and yellow Macaw. None of the Parrot tribe possess the 
. cross-bone which usually divides the opening at the bottom of 
the tube in other birds. The bronchi are triangular in shape 
and very short, extremely flexible, being. made up principally of 
membrane with slender semicircular cartilages placed at consi- 
derable distances from each other, having a broad surface of 
membrane only between the lower edge of the moveable bones 
of the tube, and the first bronchial cartilage, to facilitate the 
requisite alteration in the length of the bronchial tubes. The 
inner membranes of the bronchi unite at their upper broad 
edges to form their own. division. between the. bronchiee in the 
absence of the cross-bone. - t eir 
- The 
