quill before shaping it into a pen. Young feathers, plucked before their perfect state, are always known by the vascular pulp, gorged with blood, which fills the yet soft barrel, as our readers must have often noticed. Besides the parts of a feather above described, we must not forget to notice the accessory plume. This, observes a learned contributor to the Transactions of the Zoological Society (see vol. i. part i. p. 13), " is usually a small downy tuft, which not only assumes a very different character in the feathers of different species, but is even very dissimilar in the feathers of different parts of the body of the same bird. The accessory plume is situated at the distal (farthest from the body) end of the quill, at the aperture through which the shaft and its lateral fibres have passed out, and at the central point from which the two lines of the web begin to diverge. In the strong feathers peculiar to the wings and tail it remains a small tuft of down, as at first mentioned; but in the feathers of the body on the hawks, grouse, ducks, gulls, and some others, it is found to be of all sizes, augmented in some species to the full extent of the feather from which it emanates. The four species of struthious birds afford remarkable instances of the variety that occurs in this accessory plume. ..... In the ostrich the feathers have no accessory plume; in the rhea there is a tuft of down; in the emu the accessory plume is augmented to the full size of the principal shaft, and the web and the feather of this bird is constantly and correctly represented as having two plumes on one quill. In the cassowary, besides the double shafts and webs from a single quill, as in the emu, there is still an accessory plume, thus forming three distinct parts."

In connexion with the plumage of a bird, is the adaptation of its anterior limbs as organs of flight: these terminate neither in hoofs nor claws; they are neither organs of terrestrial support nor of prehension; they are solely fans, with which to beat the air, and raise the body by repeated strokes. They consist in the skeleton of the humerus or shoulder-bone, the two bones of the forearm, namely the radius and ulna, and a part analogous to the hand which consists of a distinct thumb, and the

vestiges of two rudimentary fingers. These bones form the solid framework for the support of the large feathers essential to flight; those arising from the hand being termed primaries; those from the fore-arm, secondaries; those from the humerus, scapularies; and those from the thumb, the winglet or bastard wing; these last are generally only four or five, and are small and rigid. Such is the general outline of the wing.

The wings of a bird, however ample, would be comparatively of little service, unless the whole structure and mechanism of the frame accorded with the design for which these organs were intended. They are the organs of flight; and now let us see what correspondence we can trace in the general mechanism of the body. Let us take a pigeon, a bird familiar to us all, as an illustrative example. How beautifully boatshaped is the body, the small head and pointed beak forming the prow, and the broad expanded tail the rudder! and what shape could be found better adapted for overcoming the resistance of the air, than that which partakes so nearly of the character of the wedge? Suppose the body had been long and slender, like a snake's, where would have been that central point of gravity requisite for maintaining an even steady course? Suppose it had been round, where that power of cleaving the sky like an arrow? No shape, in fact, could be imagined as an improvement.

The boat

like form, the oar-like wings, instruments at once of aerial support and progression; the rudder-like tail, increasing the relative surface of the body without adding to its weight, and acting at the same time as a helm in the hand of the pilot, combine to form a whole which all the ingenuity of man cannot improve, and which at once proclaims the architect to be Divine. But let us next suppose the skin, with its plumage removed, so as to exhibit the muscles beneath. How firm, how large, how powerful are those destined for the motion of the wings; they constitute the solid mass of the whole chest, and are more in volume than all the others put together. The chief developement of muscular power is here concentrated; and with good reason; for what does the

swift-winged bird want with a heavy mass of muscles on the thighs, or other parts? Enormous strength there, would be a useless gift, and the increase of weight would only be an impediment.

Let us next survey the skeleton; and here several points demand attention. First we notice its lightness. That this is an essential quality in a bird, will at once be understood; but how is this lightness of the bones compatible with the necessary degree of strength? Their lightness and their strength are both secured upon true mechanical principles; namely, by making all the bones, which require strength, such especially as those of the limbs, hollow cylinders; take for example a humerus or shoulder-bone: now if the same weight of matter which enters into its composition had been formed into a solid piece, of the same length, it would have been but a feeble lever, altogether insufficient for the strain it has to bear, and liable to snap at every stroke; on the other hand, if the bone, as it now is, had been solid, then the weight would have been objectionable; but by making it a hollow cylinder every advantage is secured; strength and lightness are combined. Secondly, the hollowness of these bones (for they are not filled up with marrow as are those of mammalia) is instrumental in another way, in rendering birds more completely adapted for their aerial mode of life. They are reservoirs for air, and communicating immediately with the lungs. The lungs of birds, unlike those of mammalia, are not floating free in the chest, but extend down the spine, to which they are attached, and fill up the hollows between the ribs at their junction with the spine: their texture is firm, and consists of distinguishable cells. But not only do these lungs communicate with and fill the hollow bones with air, but also cavities and membranous sacks, situated in some cases immediately beneath the skin on the throat, on the chest, or along the wings; in others between the muscles of the chest, and along the course of the tendons down the humerus. The design of this apparatus appears to be twofold; first, to effect a more complete aëration of the blood, as necessary to the immense comparative vigour

of the muscular system, which aëration could not be so well effected in the lungs alone, especially considering that, during rapid flight, when muscular energy is most needed and most expended, the action of breathing would be at best but imperfectly performed; and hence is this laboratory, or, in other words, this extension of lung carried throughout the body, so that the blood over an extensive surface may be constantly subjected to the mysterious agency of oxygen.

The second purpose seems to be, to increase the relative lightness of the body, in the surrounding atmosphere. The air which fills these bones and membranous cavities is necessarily rarified, so that they constitute in this respect an apparatus, analogous to a balloon, and which at least tends to the body's buoyancy.

We cannot pass from the skeleton of birds without remarking on a few of its most prominent details.

The wings, as organs of flight, have already been noticed; there is, however, a bone immediately connected with their action which demands our notice; it is that

commonly known under the name of merrythought (os furcatum). This bone is decidedly analogous to the collar bones in man, serving to keep the scapulæ steady, and the shoulders at a due distance, counteracting the tendency to approach which the action of the wings in flight produces. The bird, however, possesses accessory clavicles, or collar bones, which are long and narrow, uniting at one end with the scapulae, and at their point of junction assist to form the cavity into which the head of the humerus is received. The inferior limbs, or organs of progression on the earth, consist of the following parts; namely, the thigh bone, or femur, which is short, lies close to the body, enveloped in muscles, covered with the skin, and concealed beneath the feathers, so that it easily escapes superficial notice; hence the term thigh is often but erroneously given to the succeeding portion, composed of two bones, namely, the tibia, and a slight imperfect fibula or small-bone, running only two thirds the distance of the former; the union of these two bones to the femur, at the knee joint, is so managed that, by a spring-like ligament, the extension of the limb is maintained without any effort on the part of the muscles. The next part is the tarsus (often called the leg), which consists of a single elongated bone, covered with scaly skin alone; to its extremity are articulated the toes, upon as many pulley-like processes. The toes, in most birds, are three before and one behind, but in this respect there is much variety. Subjoined (see p. 11) is a sketch of the limb of a bird, exhibiting the bones composing it. A, the femur, or thigh-bone; B, the tibia; C, the fibula, which is merely rudimentary, as in many quadrupeds. In man it is perfect, and popularly known as the small bone of the leg; D, the tarsus, consisting of a single bone; E, the toes, generally three before and one behind. From the pelvis or hip-bone, with which the femur is articulated, arise certain muscles, the tendons of which pass by the knee and heel, and are inserted into the toes; whence the weight of the body alone firmly bends the toes, without voluntary exertion; a wise and benevolent provision of the great Creator for enabling the bird to sleep upon its