92 
BRITISH SWANS. 
PLATE II. * 
In the accompanying plate we hare endeavoured to 
shew,the principal external distinctions of the four 
species of swans which occasionallyvisit this country. 
The plumage of all of them is so similar, that with- 
out noticing the differences of the hill and head, or 
comparing the structure of the trachea and its con- 
volutions, there is great difficulty in distinguishing 
them. 
THE MUTE OR TAME SWAN, 
Oygnus olar, 
PLATE II* Fig. 2, 
Is easily distinguished from the Hooper, or Betcick’s 
Swan, by the distribution of the colours on the 
bill. In the two last the apical half of the bill is 
black, the base yellow in different proportions, 
while in the domesticated bird the reverse is the 
case, the bill being of a rich reddish orange, the 
nail, base, space between the eye, and tubercle or 
knob, black ; internally the trachea is simple, and 
enters directly into the cavity of the body, conse- 
quently the sternum has no hollow in its keel for 
its reception. 
