INTRODUCTION. 19 
An opera-glass, if a sufficiently strong magnifier, or occasion- 
ally a telescope, will be found very useful, as it enables one to 
recognize a bird without disturbing it, and to distinguish colors, 
when the object is distant, or at a great height among branches. 
It is more difficult to distinguish colors just before or after 
sunset than at other times of the day, particularly if they be ex- 
posed to the sunlight. That hour should therefore be avoided. 
§T. Of anatomy and details of structure I shall not here 
speak at length, since they are not referred to in this volume 
more often than convenience requires.14 The bill consists of 
two mandibles, the line between which is called the gape or 
often the commissure. The true cere, which belongs only to 
the parrots and birds of prey, is a thick skin which covers the 
upper mandible at its base, and in which are the nostrils, 
though often concealed by feathers. 
The principal wing-feathers are the primaries, which (with 
perhaps exceptions) are always nine or ten, except in flight- 
less birds, and which form the end or “point” of the wing. 
They are the long outer feathers, of which the shafts (if the 
wing be spread) are more or less parallel, forming an evi- 
dent angle with those of the adjoining secondaries. A so- 
called ‘‘ spurious” primary is usually the first or outermost, 
when very much shorter than the rest. (It differs from the 
‘bastard wing” or ‘‘ spurious quills” in being a single feather 
and beneath the second primary.) The “ shoulder” of the 
wing is the “bend” near its connection with the body. The 
tail is even or square, rounded or forked, as viewed when 
half-closed; if slightly forked, emarginate, if very deeply 
14 The reader is referred for a full treatise te the introduction of Dr. Coues’ 
“Key to N. A. Birds.” 
