General Characters. 
BIRDS. General Characters. 231 
chest in birds is arranged, so as to give it the firmness 
necessary to hear the strain thrown upon it in the 
action of flight, we may now proceed to the considera- 
tion of the structure of the wings, and the mode in 
which they are supported. From the articular sur- 
faces already mentioned as existing on the anterior 
part of the sternum, there spring two large and strong 
bones, which are directed upwards and forwards, at the 
same time diverging more or less from each other. 
These are the coracoid bones, which, in the Mammalia, 
with the exception of the monotremata, are reduced to 
a rudimentary condition, and anchylosed to the upper 
part of the shoulder-blade. The superior part of each 
coracoid bone is furnished with an articular surface, 
which assists in the formation of the shoulder joint. 
The remainder of this socket is formed by the ex- 
tremity of the scapula or shoulder-blade, which rests 
against that of the coracoid bone. The scapula is 
usually elongated and leather slender, and is applied 
upon the dorsal surface of the ribs, where it lies nearly 
parallel to the vertical column. From the position 
and strength of the coracoid bones, they are evidently 
well adapted to furnish firm points of support for the 
rvings ; but they are further assisted in this office by 
the clavicles or collar bones, which are usually anchy- 
losed to each other in the median line, so as to form a 
single V-shaped bone called the furculum* The 
other extremities of the clavicles are articulated to 
the inner surfaces of the superior extremity of the 
caracoid bones, to which they serve as supporting 
buttresses, and thus assist materially in resisting the 
action of the powerful muscles of the wings. The 
bones of the wings themselves are easily recognized as 
corresponding with those of the anterior members in 
the Mammalia. The humerus, or arm-bone, is a long 
cylindrical bone articulating with the shoulder-blade 
and coracoid by a ball and socket joint, and presenting 
at its lower extremity a double articular surface for the 
reception of the two bones of the fore-arm. The latter 
are usually longer than the humerus, cylindrical in 
form, and thickened at the two extremities ; but one 
of them — the ulna — is always much stouter than the 
other — the rar/fMs— which is generally very slender. 
The carpal bones forming the wrist, are two in num- 
ber, small, and rounded. They are followed by two 
elongated metacarpal bones of unequal thickness, 
which are completely anchylosed together at both 
ends. At the base of these, on the outer edge, we find 
another small bone, which is sometimes fiiee and 
sometimes anchylosed to the metacarpal (fig. 137). 
This is the rudiment of a thumb, and gives support to 
a few feathers, forming what is called the pinion or 
bastard-rving. The metacarpal bones are followed by 
the phalanges, which usually represent two fingers, 
one of which is composed of two or three joints, the 
other only of one. These phalanges are endowed with 
but little mobility, so that the whole wing may be 
regarded as composed of three joints, rmited by a more 
or less hinge-like articulation at the elbow and widst. 
By tills arrangement the wing is rendered stiff when 
extended, whilst, at the same time, its three joints lie 
* This is the well-known merrythought, with the ceremony 
of breaking which most of our readers are probably acquainted. 
nearly parallel to each other when the wing is con- 
tracted, and thus occupy a very small space. 
The structure of the hind limbs corresponds, in like 
manner, with that of the same members in the Mam- 
malia. Tlie femur, or thigh-bone, is usually short and 
stout, and articulates with the pelvis by a ball and 
socket joint, the rounded head being set on, as in the 
mammals, nearly at a right angle to the axis of tlie bone 
(see fig. 135, Plate 31). This is folloived by the tibia, 
or shank-bone, usually much longer than the tliigh, 
and accompanied by a slender fibula. This latter bone 
is, however, commonly attached to the tibia, and 
it always becomes gradually attenuated towards the 
apex, and disappears entirely long before reaching the 
extremity of the shank. The knee-joint is furnished 
with a small knee-cap, or patella. The tarsus also 
consists of a single cylindrical bone, often ot great 
length ; and the foot is terminated by from two to 
four toes containing a variable number of joints. The 
usual number of toes, especially in the most typical 
birds, is four ; and of these one is generally directed 
backwards. 
Of the muscles by which the apparatus of bones 
just described is set in motion, we need say but little. 
Tlrey are generally very firm, and of a deep-red 
colour. The principal mass of the muscles is devoted 
to the movement of the wings. Tliesc, of course, 
vary in bulk according to the power of flight possessed 
by the bird, and correspond with the development of 
the sternal keel. The muscles of the thigh and shank, 
are also largely developed, and it is in the hinder 
limbs also that we find tlie sinews presenting most 
distinctly those peculiarities which characterize them 
in birds. They are exceedingly white and glistening, 
and have a great tendency to become ossified. The 
long tendons which pass down the back of the tarsus 
from the flexor muscles of the toes, are especially 
remarkable in these respects. They are of the greatest 
importance to the bird in perching ; indeed, it is to 
this peculiar arrangement that the bird is enabled to 
perch. Passing over the back of the heel, like a cord 
over a pulley, they are necessarily stretched by the 
flexion of this joint, caused by the weight of the body 
in the act of perching. They thus exercise a sort of 
involuntary action upon the toes, causing them to grasp 
any object rvith great firmness, and thus retaining the 
bird securely in its position even during sleep. 
It is hardly necessary to say that the clothing of 
the skin in these animals consists of feathers, a circum- 
stance from which de Blainville proposed to name the 
class Penniferes. It may be as well, however, to give 
a few details of the nature of these tegumentary appen- 
dages, which, although somewhat analogous to the 
hairs of the Mammalia,' are of a far more complicated 
structure. 
A feather ordinarily consists of two distinct portions 
— a central shaft or stem, and a pair of webs, occupy- 
ing the two sides of the shaft, and composed of numer- 
ous flattened fibres or barbs, closely applied to each 
other. The basal portion of the central stem, which 
is partially inserted into the skin, is a hollow, homy 
tube, usually transparent, and terminating in a more or 
less pointed or rounded extremity. The upper portion 
