TKACHEA 983 
TRACHEA or Windpipe, the flexible tube, composed of a 
great number of rings, originally cartilaginous but ossifying more 
or less with age, through which Birds breathe and utter most of 
their characteristic notes. Its upper end is modified into the 
LARYNX, and it continues subcutaneously down the neck to the 
thorax, which it enters between the two branches of the FURCULA, 
and bifurcates into the two BRONCHI, each of which passes to the 
LUNG of its own side. The tracheal rings frequently overlap each 
other in various ways, and, except a few adjoining the larynx, are 
dorsally complete ; but in Dromexus several in the third quarter of 
the length of the tube are incomplete ventrally, and permit its 
inner mucous lining to bulge out so as to form the pouch before 
mentioned (EMEU, p. 214) which occurs in both sexes and may 
be 12 inches in length. In the T'rochili, Platalea, many Tubinares 
and Sphenisct a great portion of the tube is divided by a median, 
vertical, cartilaginous septum, extending forward from the bronchial 
bifurcation, and consisting of rings which pass laterally into those 
of the walls, thus perpetuating a condition that in other Birds 
exists for a short time only in their embryonic development, before 
the septum has been reduced to the pessulus marking the beginning 
of the bronchi. Frequently the Trachea is depressed or flattened 
dorso-ventrally, as in Psittaci, Accipitres, Ciconiw and Ratitx ; but a 
very common feature, found in many groups not at all allied to 
each other, is the dilatation of a portion, generally near the middle, 
as may be seen in several Cotingidx, Chauna and the males of many 
Anseres—some of the last-named group presenting even a second 
dilatation, which may be as in (demia fusca close to the larynx,! 
but is more usually near the lower end. Still further modifications 
are exhibited by the males of many or most of the Anseres, some 
6 or 8 of the lowest rings being fused together and forming what is 
known as the bulba ossea or labyrinth. Its simplest form seems to 
be that presented, according to Eyton (Monogr. Anat. p. 125, pl. ii. 
fig. 2), by Anas or Querquedula formosa, where the enlargement is 
very slight, but essentially similar to that found generally in the 
genus Anas? and its many subdivisions, the GARGANEY (p. 309 ®) 
1 This structure is, so far as known, quite unique: the enlargement next to 
the larynx surrounds the tube which communicates with it by an aperture on 
each side. The lower enlargement, in shape of a flattened bulb, is formed of 
expanded tracheal rings firmly ossified together. It is the more remarkable 
since the allied @. nigra has a very simple trachea. The male of Aletopiana 
peposaca has a bulbous enlargement just above the middle of the trachea very 
similar to the lower one in @. fusca. 
2 The statement (Proc. Zool. Soc. 1871, p. 651) as to the female of A. punctata 
possessing a labyrinth originated in a mistake (op. cif. 1882, p. 454). 
3 Since the footnote on this page was printed Mr. Lucas has most obligingly 
examined the labyrinth of . discors, which has uothing exceptional about it. 
