Mr. YAnRELL on the Trachee of Birds. 387 
the latter diminishing from six inches in the first to four and 
a half in the Tufted Duck, three inches in the Long-tailed, 
and but two in the Golden Eye. ‘The ribs of the birds of this 
division are elongated ; the keel of the breast-bone gradually 
decreases in depth ; the position of the wings is more forward, 
the legs placed further back. The trachez of these Ducks 
are particularly distinguished from those of the others by the 
enlargement at the bottom of the tube being covered with a 
delicate membrane, supported by slender portions of bone; the 
trachea of the Red-crested Duck (Tas. XV. e.) is an example 
of this form, and may be considered the type of this divi- 
sion. As the Egyptian Goose has in this arrangement been 
considered the link between the Geese and the first division 
of the true Ducks, from its possessing, with the characters 
of the former, the bony enlargement of the trachea com- 
mon to the latter; and the Velvet Duck, for similar reasons, 
supplying the link between the two divisions of true Ducks, 
possessing, among other characters, an altered form of the 
bony enlargement of the trachea of one, with the lobated 
toe of the other; so the Golden Eye, the last of the series, 
appears to complete the arrangement, by exhibiting some of 
the characters found in the Mergansers, which are next in suc- 
cession. The first point of similarity is in the elongated feathers 
on the top of the head, forming a crest; they agree also in the 
shape of the sternum, and a particular extension of its posterior 
edge, becoming an ensiform process, the appearance of which 
in the Goosander is represented in Tas. XV. marked (g): 
and this extension of the edge of the breast-bone prevails in 
the species of the genera Colymbus, Alca, and Uria; and with 
the elongation of the ribs observable in all good salt-water 
Divers, seems intended as a protection to the important viscera 
of the abdomen, and enables them to resist pressure when below 
the 
