34 Ornithology. 



1. That which is composed of two distinct parts, one a 

 compressed chamber, more or less covered with a thin mem- 

 brane, situated on the left side of the windpipe, wfien in its 

 proper place within the bird, which is called the drum, 

 {tympanum,) at the back of which is another chamber, formed 

 by the junction and inosculation of the base of the true 

 divarications, the cartilaginous or bony wings of which are 

 more or less united by ossification. This part has been 

 termed a bony box, [orca,) from its being usually ribbed like 

 a dice box, or the exterior and interior box. From the bot- 

 tom of the exterior box, the flexible part of the right bronchial 

 tube issues; the left bronchial tube arises from the base of 

 the drum, and is not in immediate contact with the interior 

 box, so that the respired air must first pass into the cavity of 

 the drum, in order to be received into the lungs. 



2. The labyrinth belonging to the grovelling ducks is much 

 more simple ; it consists of either one or two subglobular 

 bony chambers, which have been called ampulla. 



In most species of this division there is only one ampulla, 

 and that is situated on the left side ; but in the sheldrake 

 there are two ampullae, one on each side. Where there is 

 only one ampulla, the right bronchial tube is connected with 

 the windpipe ; the left proceeds from the base of the am- 

 pulla. Where there are two ampullae, the bronchiae are 

 partly connected with the bony base of the windpipe, and 

 partly with the ampullfe, so that there is a free circulation of 

 respiring air through those chambers. 



The structure here described will be better understood by 

 plate ii. 



A represents the trachea of the white eye, (F. nyroca,) 

 a the tympanum of the labyrinth — b the bony arch that 

 crosses the tympanum — c the bronchiae. 



B labyrinth reversed — a the back of the tympanum — c the 

 exterior orca — b the interior orca. 



C trachea of the Anas glacialis — a the opening of the base 

 covered by a transparent membrane — b the tympanum of the 

 labyrinth — c the bronchiae. 



D labyrinth of the same reversed, showing the insertion of 

 the bronchiae. 



E labyrinth of the Summer Duck, (A. sponsa,) showing the 

 front of the ampulla. 



ExTERXAL PARTS OF BiRDs. The external parts of a bird 

 which require to be noticed and distinguished by the natu- 

 ralist, are the head, neck, body, wings, tail and legs; which 

 parts are subdivided more or less minutely according to the 



