General Charactkrs. BIRDS. General Ciiaractehs. 
2:33 
pulsion. The bases of the tail feathers are concealed, 
like those of the wings, by softer feath ers, forming cowrts; 
these are usually of moderate or small size, but some- 
times attain an extraordinary degi-ee of development. 
It seems almost unnecessary to indicate the beautiful 
adaptation of the covering of birds to their habits and 
mode of life. Organized as they are for the most rapid 
passage through the air, their numerous feathers, lying 
one over the other and all directed backwards, offer no 
impediments to their flight ; whilst, at the same time, 
the very pressure of the atmosphere, as the bird pursues 
its swift course, will only cause the feathers to lie more 
closely, and thus present an increased obstacle to the 
penetration of the cold air to the skin of the bird — a 
circumstance of no small importance wiien we consider 
the high temperature of the bodies of these creatures. 
The dowy coat which everywhere intervenes between 
tire external feathers and the skin, is an additional pro- 
tection against the influence of cold, especially by 
giving room for a certain quantity of warm air, the 
escape of which is prevented by the outer feathers. 
The structure of all the feathers, even those of the 
wings and tail, renders them very light, a necessary 
condition for animals whose principal activity is in the 
air. In the aquatic birds a further provision is necessary ; 
the feathers of these must resist the passage, not only 
of air, but of water. For this purpose they are found 
to be constantly lubricated with a peculiar oily secre- 
tion, which renders them perfectly waterproof; it is 
obtained from a peculiar gland situated on the tail, 
which the birds press wth their bills when cleaning and 
arranging their plumage. 
In most birds the whole surface, with the exception 
of the bill and feet, is clothed with feathers, but a few 
have the head, or even the head and neck, quite bare. 
In most of these the skin is folded so as to form wrinkles 
or wattles, which are often adorned with the most bril- 
liant colours. 
The horny bill or beak which incloses the jaws of 
all birds, is usually of a more or less conical form ; but 
this is modified almost infinitely to suit the requirements 
of the different species. Thus, in the hawks or other 
predaceous birds, the upper mandible of the bill is 
strongly hooked at the tip, and many of the species 
possess a tooth on each side at some little distance 
from the apex ; the parrots possess a strongly hooked 
bill, which assists them in climbing ; the wading birds 
are often endowed with long bills, adapted for the cap- 
ture of their food in mud and water ; and the ducks 
have a more or less flattened bill, fringed along the 
margins, and admirably fitted for straining their food 
from the soft mud in which it is often found. All 
these and many other variations in the form and struc- 
ture of the bill, will, however, come under our con- 
sideration hereafter, in describing the characters of 
the different species of birds, so that it is unnecessary 
to dwell upon them any longer here. The cere is a 
naked skin, clothing the base of the bill in many birds, 
and inclosing the nostrils. 
In the structure and clothing of the feet, we find 
characters of perhaps equal importance with those pre- 
sented by the bill and wings. The number of toes is 
usually four, and of these three are commonly turned 
VoL. 1. 30 
forwards, and one — the great toe — backwards. In some 
of the waders and aquatic birds, the hind toe is entirely 
wanting, as it is also in the ostriches ; the true, or 
African ostrich, is also destitute of one of the front 
toes, so that it has but two in each foot. In the parrots 
and woodpeckers, and some other climbing birds, the 
outer toe is directed backwards as well as the great toe, 
so that there are two each way — (see fig. 134) — and 
the cuckoo has the power of turning the outer toe 
either backwards or forwards at its pleasure. The 
swifts have all the four toes turned in one direction. 
In most birds the toes are united at the base by a small 
fold of skin or web, which is generally insignificant, but 
often shows itself k'ery distinctly. In the true water 
birds, these webs attain a much larger development, 
generally uniting the anterior toes quite down to their 
tips, and in some cases even extending back along the 
inner margin of the foot to the hinder toe. 
In a few birds, of which the eagle is one, the clothing 
of feathers extends down to the very toes, but in the 
majority the whole foot, from the heel downwards, is 
quite naked, and in some of the waders and water birds 
this naked part even extends for some distance up the 
shank. The skin of the foot is of a horny texture, 
sometimes scaly or gTanulated, sometimes divided into 
distmet horny plates of larger or smaller size. The 
toes are always terminated by claws, the form of which, 
like that of the bill, usually furnishes a good clue to the 
habits of the animal. Thus, in the predaceous species 
we find the claws long, strong, sharp, and curved, 
forming most formidable weapons ; the smaller grani- 
voi’ous and insectivorous birds are also usually provided 
with long, curved claws, but these are slender and 
weak, and only of service to them in clinging to the 
surfaces of objects. Those species which, like the 
pheasant and our common fowl, find much of their 
food by scratching in the earth, are furnished with 
stout nail-like claws ; and these organs become still 
more nail-like in many of the aquatic birds. In the 
pheasant family, the male buds are frequently furnished 
with one or more spurs or accessory claws, attached to 
the back of the tarsus, at some little distance above the 
hinder toe. 
In their internal structure, birds present much resem- 
blance to the Mammalia ; they possess the same organs, 
arranged, with one or two exceptions, nearly in the 
same manner, and the vital operations are carried on 
by precisely the same means in both these great classes. 
The principal difference in the structure of the diges- 
tive organs consists in the dilatation of the oesophagus, 
or gullet, into a spacious bag called the a'op, in Which 
the food is retained for some time after being swallowed. 
The walls of this bag contain a gi'eat number of glands, 
the fluid secreted from which soaks the food, and thus fits 
it for the action of the true digestive organs. The true 
stomach is separated from the crop by a continuation 
of the oesophagus, furnished with very thick, glandular 
walls. The office of these glands is to secrete the gas- 
tric juice ; and the stomach itself, in those birds which 
feed on hard substances, such as seeds, is very muscu- 
lar, and lined internally with a hard coating, which 
materially assists in the trituration of the food. This 
stomach is well known as the gizzard. 
