aris).

katoo. 4. Frigate-bird. 5. Head of blue-bird (Silvia sialis). 6. Memura (Memura superba). 12. Great auk. 13. Head 10. Bird of Paradise (Paradisea apoda). II. Head of cuckoo.

of whip-poor-will. 17. Nightingale (Luscinia philomela). 18. Sea-eagle or osprey. 19. Head

are elongated feathers on the back of the neck, which the bird can erect, and even in some measure throw forward at pleasure; and these, in the genus lophorina, assume a form resembling that of a pair of outspread wings, and rise far above the head. The tail is, in general, not unlike that of a crow in its shape; but in many species there arise, from the rump, at the sides of the tail, two very long feathers, or rather filaments, covered with a sort of velvety down: of these, the common B. of P. affords an example. In the king B. of P. (cincinnurus regius), these long tail-filaments terminate in a sort of disk, as the tail-feathers of the peacock do.

Birds of P. are, in general, more or less gregarious. They sometimes pass in flocks from one island to another, according to the change of seasons, from the dry to the wet monsoon. Owing to their plumage, they fly more easily against than with the wind, and by high winds they are sometimes thrown to the ground. They are lively and active, and in confinement pert and bold. They bestow great care upon their plumage, and sit always upon the perches of the cage, so that no part of it may reach the floor, or get in the least degree soiled. It has seldom been found possible to bring them alive to Europe, and they seem very incapable of enduring any other than a tropical climate. In confinement, they are easily fed on rice, insects, etc. In a wild state, their food consists in great part of the fruit of the teak-tree, and of different species of fig, and also of the large butterflies which abound in their native islands.

The Papuans kill birds of P. by shooting them with arrows, and employ various other means of taking them for the sake of their skins. The skins are dried in smoke, and fumigated with sulphur, to preserve them from insects; and in this way the brilliancy of the color is impaired, so that the most gorgeous plumes which are ever seen in Europe are inferior, in this respect, to those of the living bird. The skin, to which great part of the flesh is allowed to remain attached, is always much contracted by this drying process, and a very erroneous notion is therefore often formed of the size of the bird. The common B. of P. is as large as a jay. It is of a cinnamon color, the upper part of the head and neck yellow, the front and throat emerald green, the shoulder-tufts yellow. The whole length of the extremity of these is not less than two feet. Another nearly allied species (Paradisea rubra) has these long feathers of a brilliant carmine color.

BIRDS (Aves), the fourth class of vertebrated (q.v.) animals, and the first of oviparous veterbrated animals, including all the oviparous animals which have warm blood. B. exhibit great similarity in their general structure, and are sharply distinguished from all other classes of animals. To this class belong all animals, except bats (q.v.) alone, which have an internal skeleton, and are capable of true flight. The anterior extremities of B. serve them only as wings or organs of flight, and never in any degree as arms or legs; those few birds in which the wings are too small to raise the body in the air, generally employ them to aid their swift running upon land, as the ostrich, or for swimming under water, as the great auk and the penguins. The body is covered with feathers (q.v.), and this is one of the characters in which all birds agree, and by which they are distinguished from all other animals. The general form is adapted to motion through the air, and the trunk is compact, and somewhat boat-shaped. The vertebral column possesses little flexibility; indeed, the vertebræ of the back generally become ankylosed or firmly united together by cementing bone, the solidity which is thus acquired being of evident use for the support of the ribs, and these also are proportionately stronger than is usual in quadrupeds; each of them is provided in the middle with a flattened bony process, directed obliquely backwarks to the next rib, so that they support one another, whilst instead of being united to the sternum, or breast bone, by cartilages, as in quadrupeds, they are continued to it in the form of bone; all these things combining to give strength to that part of the body in which it is particularly needed, both in order to the powerful action of the wings, and the perfect freedom of respiration during flight. In those birds, however, which do not fly, the vertebræ of the back retain some power of motion. The hinder part of the vertebral column exhibits a solidity even greater than its anterior part, the lumbar vertebræ (see SKELETON; SPINAL COLUMN) being consolidated with the pelvis (q.v.), which furnishes attachment to strong muscles which support the trunk upon the legs, and give motion to those members. The vertebral column, however, terminates in a number of small movable (coccygeal) vertebræ, the flexibility of this part being necessary to the motion of the tail, which is itself supported by a short and generally much elevated bone, regarded as consisting of ankylosed vertebræ, called the rump-bone, or, from its peculiar form, the plowshare-bone. In contrast to the general stiffness of the vertebral column in the trunk, it is remarkable for great flexibility in the neck, enabling a bird to make ready use of its bill, or to bring its head into such positions as suit the adjustment of the centre of gravity in flying, standing, etc.

The number of vertebræ in the neck varies from ten to twenty-three, the smallest number being greater than is found in any quadruped. The head, also, is so articulated to the neck, by a single condyle, or pivot, that a bird can turn its head round in a manner impossible to the mammalia. The skull itself is formed of bones corresponding with those of man and quadrupeds; but they can only be distinguished when the bird is very young, soon becoming consolidated together. The jaws are much elongated, so as to form the bill, the organ chiefly employed in seizing food, as well as for fighting, nest

building, dressing or preening the feathers, and instead of a hand for every purpose which bird-life requires. The upper mandible of the bill is so connected, however, with the bone of the skull, by elastic plates, that it possesses some power of motion, and any shock which it may receive is much deadened before reaching the skull. The bill affords many of the most important distinctive characters of B., differing very much according to the mode of life of different orders and tribes. See BILL.

The sternum or breast-bone in B. is remarkably large and strong, serving for the attachment of the powerful muscles which depress the wings, and receives great attention from naturalists, because its variations correspond with the differences in some of the most important characters and habits of birds. It generally exhibits a projecting ridge along the middle, which is proportionately largest in birds of most powerful flight, and is wanting only in ostriches and a few other birds of allied genera which do not fly. The clavicles or collar-bones, also, are generally united to form the fourchette (furcula) or merrythought bone, serving, along with two bones called the coracoid bones, to keep the shoulders separated, and to resist the compressing tendency of the action of the wings. The bones of the wing itself are regarded as corresponding to those of the anterior extremities in man and quadrupeds; the bones of the hand, however, being much disguised, and some of them wanting or rudimentary. In the accompanying cut of the bones of a bird's wing, a is regarded as the elbow-joint, b as the wristjoint, c as the knuckle-joint, d being the representative of a finger, e and f the rudimentary representatives of two others, whilst the winglet, g, formerly regarded as representing the thumb, is now rather supposed to be homologous to the forefinger. The wings, therefore, exhibit a structure entirely different from those of bats, in which the fingers are extremely elongated. The surface necessary for striking the air is provided by feathers larger and stronger than those of other parts of the body, called wing-feathers, quill-feathers, or quills. Of these, which exhibit an admirable combination of strength with lightness and elasticity, some spring from the part of the wing between b and d (in the figure of the bones of the wing); these are always the largest, and are called the primary wing-feathers, or simply primaries; those which spring from the part between a and b are called secondaries; and those which spring from the part between a and the shoulder-joint are called tertiaries. At the base of the quills, on both sides of the wing, are feathers called wing-coverts, and these are likewise distinguished as primary, secondary, etc. The feathers which grow over the shoulder-blades are called scapulars. The feathers of the wings vary in length and strength, according to the mode of life and power of flight in different B.; narrow, sharp, and stiff wings being indicative of swift and enduring flight. The tail-feathers serve the purpose of a rudder to guide the bird, and also that of balancing it in the air; they resemble in character the quills of the wings. They are also furnished with coverts above and below. Some B. have the tail rounded at the extremity; in some, it is square; in others, notched or forked. In many land B., the tail exhibits ornamental plumes, and remarkable developments of the plumage take place also in other parts of the body, in the form of crests, ruffs, shoulder-tufts, etc.

Skeleton of bird's wing.

The legs of B. consist of parts corresponding to those found in man and quadrupeds; but the thigh is short, and so concealed within the body, that it is not apparent as an external portion of the limb; the next division, often mistaken for the thigh, being the leg strictly so called, or tibia, which ends at what is really the heel-joint, although popularly regarded as the knee; and beneath this is the shank or tarsus, which in some B. is very long, serving as a part not of the foot but of the leg, and formed by a single bone which represents both the tarsus and metatarsus. The feet are divided into toes, which are generally four in number, three before and one behind, differing from each other in length and in the number of joints or phalanges of which they are composed, the toe, which is directed backward, being in general comparatively short, and consisting only of two joints. A fifth toe or tarsal spur is found in some of the gallinaceous B.; and in some B., as bustards, the hind-toe is wanting; the ostrich has only two toes, both directed forward, with the obscure rudiment of a third; and numerous B. classed together in the order of climbers (q.v.) or yoke-footed B., including parrots, cuckoos, woodpeckers, etc., have two toes before, opposed by two toes behind, the foot being thus particularly adapted for grasping, so that parrots, as is well known, even use it as a hand. The feet of B. vary considerably according to their mode of life; and naturalists therefore depend very much upon them in classification. In some the claws are strong and hooked; in others short, straight, and weak; in some the toes are all separate, in others more or less connected; in B. specially adapted for swimming, they are generally webbed or united by a membrane; in other swimming-B., however, a membrane only extends along the sides of each toe. In most B. the tarsus is feathered to

the heel-joint; in some, however, and particulary in waders, the lower part of it is bare; the shank and toes are generally, although not always, destitute of feathers, and are covered with a scaly skin. Almost the only other parts of a bird often destitute of feathers, are the cere at the base of the bill, and the combs and wattles of gallinaceous birds.

In order to flight, it is indispensable that the center of gravity of a bird should be under the shoulders; and when a bird stands, the feet are brought forward, and the head thrown back, so that the claws project beyond a vertical line passing through the center of gravity of the whole body. This is generally accomplished so that the trunk is in an almost horizontal position, the fore-part only a little elevated; but in some B., which have a short neck and short legs, an errect attitude is necessarily assumed, so that the penguins of the southern seas present to navigators a somewhat ludicrous resem blance to regiments of soldiers on the beach. B., when they sleep, very generally place their head under their wing, and some of them also stand upon one foot, their equilibrium being thus more easily maintained. A remarkable contrivance, particularly to be observed in storks and other long-legged B., renders this posture unfatiguing; a locking of the bone of one part of the limb into a scrt of socket in the bone of the part above it, so that it retains its place without muscular exertion; whilst a similar purpose is served by the tendons of the muscles which bend the claws passing over the joints of the leg in such a manner as to be stretched by the mere pressure there when the weight of the bird rests upon the legs, so that without any effort the claws retain a firm hold of the branch upon which it is perched.-Flying is accomplished by the action of the wings upon the elastic and resisting air; the muscles by which the stroke of the wing is given are pow. erful, those by which it is retracted are comparatively weak. Owing to the manner in which the first strokes of the wing must be given, few B. rise with facility from a level surface; and some of them, as swallows, and particularly swifts, rise from a perfectly level surface with great difficulty, and comparatively seldom alight where they cannot find an elevation from which, as it were, to throw themselves.

The digestive apparatus of B. resembles that of mammalia; exhibiting, however, various modifications, according to the different kinds of food-some B. feeding on flesh, others on fish, others exclusively on insects, others on seeds, others more indiscrimi nately on a variety of animal and vegetable substances. Few B. masticate their food in any degree, although parrots do; upon being swallowed, it enters the crop or craw, sometimes called the first stomach, an enlargement of a œsophagus or gullet, situated just before the breast-bone, and here it is moistened by a secretion, which is also by some B.-particularly by pigeons-employed as the first food for their young, the glands of the crop enlarging very much, so as to produce it in large quantity at the time when it is wanted for that purpose. The crop is wanting in the ostrich, and also generally in B. that feed on fish; and is of greatest size in those of which the food consists of seeds or grain. It is generally single, and on one side of the gullet; sometimes, as in pigeons, it is double. A second stomach, or dilatation of the esophagus, called the proventriculus or ventriculus succenturiatus, is generally largest in those B. in which the crop is wanting or small; and in this the food is further softened and changed by a secretion which is mixed with it. The third and principal stomach is the gizzard, which in B. of prey, fish-eating B., etc., is a mere membranous sac; but in B. which feed on grain or seeds is very thick and muscular, so that it acts as a sort of mill, and with extraordinary power. In these B., also, a remarkable provision is made for the perfect grinding down of the contents of the gizzard, by the instinct which leads them to swallow small rough pebbles or grains of sand, an instinct well exemplified in the common domestic fowl.-The liver of B. is, in general, very large. The kidneys are large, but there is no urinary bladder, and the urine is at once poured into the cloaca, an enlargement of the intestine, at its termination, with which also the organs of generation communicate in both sexes.

The respiration of B. is very perfect, and their blood is from 12° to 16° warmer than that of mammalia; its circulation more rapid, and the energy of all the vital processes proportionally great. B., consequently, exhibit great liveliness; and upon the admirable provision for the aëration of their blood they depend also for their powers of flight, which enable some of them to travel hundreds of miles with great rapidity and without exhaustion, whilst others soar to a prodigious height in the air. The heart resembles that of the mammalia in its form and structure; but the right ventricle, instead of a mere membranous valve, is furnished with a strong muscle. to impel the blood with greater force into the lungs. The lungs are small, and communicate with large air-cells (q.v.) in the cavities of the body, and even in the bones, so that the aëration of the blood takes place not only in the lungs but during its circulation through the body. An extraordinary proof of the use of these air-cells in respiration was afforded in a recorded instance of a large sea-fowl, which, when an attempt was made to strangle it, was kept alive by the air entering in a forcible current through a broken wing-bone. (Gosse, The Ocean, quoting Bennett's Whaling Voyage.) B. consume much more oxygen in propor tion to their size than quadrupeds.

The organs of the senses are similar to those of mammalia. In the senses of touch and taste, it is generally supposed that there is an inferior development, although parrots appear to possess the sense of taste in considerable perfection; and the bills of some B., which search among the mud for their food, are certainly very delicate organs of