
INTRODUCTION. 
=) IIE BIRDS constitute the Second Class 
M| of Vertebrate Animals. They resemble 
Mammalia in having warm red _ blood, 
and a complete system of circulation, for 
their heart, like that of Mammalia, contains four 
chambers, two auricles and two ventricles. But in- 
stead of bringing forth living young, birds lay eggs, 
which they hatch in more or less neatly constructed 
nests. The number of cervical vertebra is not 
limited to seven, as is almost invariably the case in 

Mammals, but increases in proportion to the length 
of the neck. But the most immediately obvious 
characteristics of birds are the conversion of the front 
limbs into organs of flight, and the feathery covering 
of the whole body, which replaces the hairy coating 
of mammals. ; 
These feathers are gradually thrown off, and 
are replaced by new ones, at least once a year. 
This generally takes place in autumn, and is called 
moulting. 
A fully developed 
feather consists of the 
quill, the shaft and 
the vane. 
consists of many thin 
layers, called barbs, 
which are linked to- 
gether by fine hooked 
processes. The feathers 
are not found upon all 
portions of the skin, 
but on definite spaces, 
which are called Pteryle 
or feather-tracts. The 
head is usually covered 
with feathers. One 
feather-tract extends 
on the lower side of 
the neck to the breast. 
There the feather-tracts 
fork. A similar feather- 
tract commences behind the head, and extends over 
‘the whole back to the tail. The feathers 
arranged, that, although placed on definite tracts, they 
form a protective covering to the whole body. 
Birds 
The vane 

Skeleton of Bearded Vullure 
are SO 



and partly with feathers. 
The bare or downy spaces (Apteria), are very 
service: ble to the bird, for they enable it to move 
its head and neck in all directions, and to cover its 
head when it sleeps. 
The wings, or fore limbs of birds are con- 
structed on the same model as the fore limbs of 
mammals, They consist of arm, forearm, and hand. 
The wings are furnished with a series of long and 
strong (quills), which serve for flight. 
The hand is composed of a thumb and two fingers 
only, and the thumb with its clothing of feathers is 
called the Alula or bastard-wing. The direction in 
flight is chiefly guided by the tail-feathers. 
feathers 
Wing-bones of Bird. 
hw e 

hw. Carpus or wrist, 
d. Pollex or thumb, 
mh, Metacarpus. 
f. Digits or fingers, 
ec. Humerus or 
s. Radius Farol arn 
c, Una f ; 
arm, 
Arrangement of Wing-feathers. 

a 
h. Primaries sd, Scapulars. : 
a. Secondaries. 1. Alula or Bastard-Wing 
w. Wing-coverts. 
On examining the legs, we find that the femur 
and the tibio-fibula are clothed partly with flesh, 
The slender tarso -meta- 
tarsus is covered with horny scales, and terminates 
1 
