Page:Pigeons - their structure, varieties, habits, and management (IA b28107901).pdf/20

 breast-bone to the humerus, and, when they contract, pull down the wing with extraordinary force. The muscles that raise the wing are not shown in this figure: they are much slighter, and, consequently, act with much less force.

The annual change of the flight-feathers takes place in the autumn. The mode in which this is arranged, so as not to interfere with the efficiency of the wing as an organ of flight, is most admirable. The moulting of the wing commences with the tenth or last flight-feather, or primary, and a new feather is produced so as to supply its place. A few days before this attains its full length, the ninth primary is shed, and subsequently the eighth, and so on to the first. The secondaries are replaced in a similar manner, only that the process commences with the first secondary and proceeds gradually to the twelfth. The effect of this arrangement is, that the efficiency of the wing as a means of flight is never seriously interfered with, as the loss of one feather at a time has no great effect in impairing the action of the limb.

The feathers of the tail are usually twelve; but in some of the domestic varieties the number is very greatly increased, occasionally to even three times that amount. The use of the tail is to support the hinder part of the body during flight. The tail, being held inclined obliquely downwards, presses, during the forward flight, against an inclined plane of air, and thus tends to raise the hinder part of the body—a support which is required, inasmuch as the wings are placed at the fore part of the trunk, far in advance of the centre of gravity of the whole body. The utility of the tail during flight is strikingly shown in the difference, with which a pigeon flies after it has lost its tail-feathers: the action of the wings is much more rapid, the flight laboured in the extreme, and the bird so mutilated is left behind by the other birds of the flock in their rapid flight. The statement that the tail can be made to act like a rudder, in directing the course of flight, is often made by compilers of works on natural history, and repeated even in a work of as high authority as Owen's "Anatomy of Vertebrates." It is, however, entirely destitute of any foundation in fact. Birds turn, during flight, by striking the air more forcibly with one wing than the other.

The general character of the plumage of the pigeons differs greatly from that of the true poultry. The tube or quill of the body-feathers is generally short, and the shaft increases considerably in size towards the middle of its length, and then diminishes very rapidly towards the end. The whole of the feathers of the pigeon are destitute of the small second feather or accessory plumule, which is found growing at the top of the tube of the feathers of the true poultry birds. These peculiarities of plumage are sufficiently strongly marked to render the recognition of the feather of a pigeon certain to an observant naturalist.

The digestive organs in pigeons, Figure V., are strongly characterized by structural peculiarities distinct from those of other birds. The bill is small, slightly curved, and covered at its base by the membrane of the nostrils, which is scurfy and bare of feathers, the nostrils themselves being long and narrow. Contrary to the arrangement that is found in most birds, the bony frame-work of the upper