THE EXTERNAL STRUCTURE OF BIRDS. 143 
covering of the front part of the head may be replaced by a 
horny plate or ‘shield,’ as in the Coot and Moor-hen. 
On the other hand, some or other of the head-feathers may 
be exaggerated in size, forming crests, which may be single and 
median as in the Cockatoo, or double and lateral, as in the 
so-called “‘horns” of Eared Owls (structures which have 
nothing whatever to do with the ears) and in the Crested 
Grebe. 
Very rarely feathers of the mentum may be elongated, as in 
the Bearded Vulture. More often those of the gular and 
malar regions with the auriculars may form “ ruffs.” 
The Bill is perhaps the most important part of a Bird’s ex- 
ternal organization for the purposes of classification. It is also 
a most important organ in the economy of the Bird’s life, for it 
not only serves for taking food, but, as already said, subserves 
the purpose of a hand or fingers, and in some cases is an organ 
of feeling, as in the Snipes and Woodcocks. The bill serves 
for picking up, carrying, cutting, tearing, or crushing, accord- 
ing to circumstances, and it is almost always more or less 
conical, generally ending in a sharp point. 
Different definite technical terms are used by Ornithologists 
to denote its form. A bill is said to be of medium length if it 
is about as long as the head. If less than that length, it is 
short, and it is long if it much exceeds it. A bill which is short 
is said to be acute if pointed at the tip. If there is a hook- 
like process at the tip, the bill is calied hamulate or wnecinate. 
It is dentate when toothed as in w Falcon, and when there are 
a number of small tooth-like processes along the margins of the 
bill, it is said to be serrate. If the bill, as in the Duck, bears a 
nail-like process at the end of the maxilla, it is termed wngui- 
culate. When the bill is extremely long and slender as well as 
pointed, it is sometimes compared with a needle and so called 
acicular, or, if less slender, to an awl, subulate. If only slightly 
elongated it is acuminate; and the term attenuate is supposed to 
denote a condition intermediate between ‘‘acuminate” and “ sub- 
ulate.” A bill which is flattened is said to be depressed, and if 
widened at the end is called spatulate (as that of the Shoveller 
Duck and, ‘still more, that of the Spoonbill). A bill rather high 
and narrow is called compressed. A bill of the most ordinary 
shape, like that of a Sparrow, is called controstral, A beak which 
is short with a wide gape, like that of the Swift, is termed jissi- 
rostral. The quite opposite condition of bill (¢.9., that found in 
