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Sight is the most perfect and most delightful of all the senses. It fills the mind with the largest variety of ideas, converses with objects at the greatest distance, and continues the longest in action without being satiated.”—SPECTATOR.
naturalist can infer the one from the other with unerring certainty.
986. Examples of the agreement between the formation of the beak and the food of the bird are furnished as follows:-Sea-birds, which feed on fish too large to
be swallowed at a mouthful, are furnished with a large beak, hooked at the end. But this instrument is much longer, and therefore less powerful, though sufficiently so relatively to their prey. When birds feed on such fishes and reptiles as are small enough to be seized and easily swallowed, the beak is straight, still greater in length and resembling a pair of pincers, as those of the martin pecker, fig. 1. Birds living on insects as the bee-eater, fig. 2, have slender and very long beaks, either straight or very slightly hooked, except when they catch their prey in flight, as do the swallow and the goatsucker, fig. 3, in which the bill is short, broad, deeply cut, so as to enable them to present a large mouth to receive
Birds which live on grain, on the contrary, such as the sparrow, fig. 4, have a short, thick bill, convex above, or conical, and in general straight, the upper mandible not projecting over the lower. A singular modification of this organ of prehen
sion is presented in the case of the 3
pelican, which has a membranous receptacle, consisting of a pouch or pocket, attached to its lower mandible, in which it collects prey, which it swallows afterwards at leisure. (See 942.)
987. Why have the eyes of birds a greater facility for discerning near or distant objects than those of other animals ?
Because, in the first place, birds in general procure their food by the aid of their beak; and, the distance between the eye and the point of the beak being small, it becomes necessary that they should have the power of seeing very near objects distinctly.
On the other hand, from being often elevated much above the ground, living in the air, and moving through it with great
“ The eye is not that which sees; it is only the organ by which we see. The ear is not that which hears, but the organ by which we hear; and so on of the rest."-Reid.
velocity, they require for their safety, as well as for assisting them in descrying their food, a power of seeing at a great distance.
988. Two peculiarities are found in the eyes of birds. The one is a bony, yet, in most species, a flexible rim or hoop, surrounding the broadest part of the eye, which, confining the action of the muscles to that part, increases the effect of their lateral pressure upon the orb, by which pressure its axis is elongated for the purpose of looking at very near objects. The other peculiarity is an additional muscle to draw, on occasions, the cystalline lens back, and to fit the same eye for the viewing of very distant objects. By these means, the eyes of birds can pass from one extreme to the other, on a scale of adjustment as convenient as it is remarkable.
989. Why is the hearing of birds dependent upon the internal structure, rather than the outward development of the organ?
Because, if the external ear existed as in quadrupeds, it would obstruct the rapid progress of birds through the air, and be inconvenient in other respects. This appendage is therefore withheld, but is amply compensated for by a peculiarity in the internal structure, which enables them to hear with perfect distinctness.
990. Why do birds perch with their faces to the wind ?
Because, if a bird were to roost with its tail to the wind it would frequently be driven from its perch : the wind would, by turning the feathers, and even getting under the wings, have great power ; and the action of that power would unbend the legs, and thereby loosen the feet from the perch. But, by perching with its head to the wind, the latter becomes a means of stability to the bird.
991. The bird keeps its hold on the perch by tendinous elasticity; the flexure of the neck is beyond that position which would be repose in a quadruped, so that the tendons of the extensors are tightened ; and any cause which agitates the perching feet, at the same instant brings the neck into action, and extends, elevates, or depresses the head, to the exact extent which the balance requires. Thus, there is, in the very structure of the bird, a means of resisting any casualty that might drive it from its perch, and that without the exercise of any more volition than accompanies the breathing of a human being when asleep.
“The starling, distinguishable from the rest of the sparrow tribe, by the glossy green of its feathers, in some lights, and purple in others, breeds in caves of houses, ruins, hollow trees, cliffs, and high rocks."-GOLDSMITH.
992. Why are birds enabled to sleep securely when perched on the branches of trees ?
Because the claws of birds are so organized, that the flexor muscles pass over the joints of the knce and heel in such a manner, that, when the latter bend, they necessarily press on the tendons of the muscles, and make them bend the toes; the weight of the body pressing down the thighs and legs, necessarily produces this action ; and, as a consequence, the bird grasps, without effort, the branch on which it is perched, and maintains itself in a fixed position without watchfulness.
993. Why do starlings frequently accompany rooks in their flight?
Because rooks have a more discerning scent than starlings, and lead them to spots productive of food.
The superior power of finding food is owing to rooks having two large nerves which run down between the eyes into the upper mandible, which invests their beaks with a more delicate sensitiveness than other round-billed birds, and enables them to grope for their food when out of sight.
994. Why are the necks of birds long, and easily moveable?
Because the beak is generally the only organ of prehension by which they pick their food from the ground ; and the extent of the neck is augmented, in order to admit of the head being brought freely to the ground without incommoding the body.
995. How is the wisdom of the Creator shown in the structure of the head and neck of birds ?
In the heads of birds teeth are dispensed with, and, as a consequence, along with them, the thick and massive jawbones into which they must have been implanted, and which are replaced by a light strong bill.
Hence mastication is very limited, and the muscles subservient
“ To these, an overgrowne justice of peace,
With a clarke like a gizzard thrust under each arm;
Set o’re a chafing dish to be kept warme.”-B. Johnson.
to this function are proportionately small. Everything thus combines to render the head light, and consequently a long and slender neck is sufficient for its support.
Had it been necessary to sustain heavier a head at the extremity of a long neck, great muscular development in this region would have been required, and the weight so much increased, as to have materially diminished the powers of flight. Moreover, the heavy head at the extremity of the lever of the neck would have deranged the centre of gravity, and in this way also have interfered with flight.
996. Why does the breastbone form an important part of the organization of a bird?
Because it imparts solidity to the whole of the framework, and supplies a wide base upon which the muscles of the wings are fastened down and steadied. The breastbone also forms a kind of box, which, during the time the body is stretched out in flight, securely retains and supports the soft interior of the bird.
The more the movements of the wings excite the great muscles which are spread over the inside of the breastbone, the more do those muscles brace and strengthen the frame of the bird. They bear its weight up to the wings, and the wings again, by their long arched form, lay it upon the air. Thus as the bird flies, it is almost insensible of the fact that its body is heavy.
997. The breast-bone of a bird secures the whole length of the body, and the great central spire of that bone, called the keel, rises from it, so as to give lodgment and attachment to the great muscles of the wings. It will be easily understood that this keel is more largely developed in birds of passage, since its greater prominence implies strength of wing for long-continued flight. Under the breast-bone, and between the back-bone, is a considerable space, occupied by air-cells. These cells represent a curious provision for the extension of the body of the bird, independently of weight. The air does not only pass into the lungs of birds, but through them, so as to fill a series of cells, composed of fine membranes, which are interwoven with all the viscera. The heart is surrounded by such a cell. Two great cells are attached to the liver, and in the same manner all the viscera of the abdomen are interspersed with air-cells, and these all communicate. The air thus admitted into the interior of the body extends even into the bones. By inflating these cells, birds have the power of instantly rendering their bodies specifically “ Thy style's the same whatever be thy theme,
As some digestions turn all meat to phlegm.”—DORSET.
lighter, and of rising upon the air with greater ease : when they descend, they exhaust the cells, and alight with greater case.
998. Why is the gizzard such an important organ in the structure of birds ?
Because it compensates for the absence of teeth, by triturating or grinding the food, so as to render it fit for digestion. Every particle of food which requires to undergo this operation, is submitted to the action of the two gristly surfaces which form a portion of the organ, and produce a rotatory motion the food.
999. In order to ascertain the peculiar powers of the gizzard, several experiments have been resorted to, some of which would appear at first sight to be cruel, but which in the end proved to be harmless. “ Twelve strong tin needles," says Spallanzani, “were firmly fixed in a ball of lead, the points projecting about a quarter of an inch from the surface. Thus armed, it was covered with a case of paper, and forced down the throat of a turkey. The bird retained it for a day and a half without showing the least symptoms of uneasiness. Why the stomach should have received no injury from so horrid an instrument I cannot explain : the points of the twelve needles were broken off close to the surface of the ball, except two or three, of which the stumps projected a little higher. Two of the points of the needles were found among the food. The other ten I could not discover, either in the stomach or the long track of the intestines; and therefore concluded that they had passed out."
In another experiment, which, without knowing the previous facts, we might justly have deemed still more cruel, Spallanzani tells us he fixed twelve small lancets, very sharp both at the point and edges, in a similar ball of lead. “They were such as I use for the dissection of small animals. The ball was given to a turkey cock, and left eighteen hours in the stomach, at the expiration of which time that organ was opened ; but nothing appeared except the naked ball, the twelve lancets having been broken to pieces; I discovered three in the large intestines, pointless and mixed with the other contents; the other nine were missing, and had probably been voided. The stomach was as sound and entire as that which had received the needles.
“Two capons, of which one was subjected to the experiment with the needles and the other with the lancets, sustained them equally well. My next wish was to know how much time elapsed before the beginning of the fractures; and by repeated experiments on turkeys I found that these sharp bodies begin to be broken, and lose their shape, in two hours. This, at least, happened in two individuals of the species : in one, four of the lancets, and in the other, three of the needles, were broken within that space; the others were blunted, but continued fixed in the balls."