314 Mr. Yaurell on the Organs of Voice in Birds. 



will 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 (Tab. XVII. Fig. 8, b) 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, Z/), 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. Tab. 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 bronchiae 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 bronchia unite at their upper broad 

 edges to form their own division between the bronchiae in the 

 absence of the cross-bone. 



The 



