Order IV.—Loricata.[9] This corselet or armor-covered family includes Crocodiles and their allied species. Their upper parts are covered with a corselet of bony plates set in the tough, leathery skin. The jaws are long, and have many strong, conical teeth, fixed in sockets. The lower jaw extends back of the cranium, and the upper is hinged and movable. Crocodiles belong in tropical climates, are sluggish animals, and live a long time if not destroyed by violence. Their legs are short but powerful, and when on land they manage to wriggle, or drag, their immense bodies along with considerable speed. They are found in India, and in all the large rivers of Africa. The Gavial of the Ganges, the Crocodile, and the Mississippi Alligator are closely related, though there are some structural differences. Of whatever variety, whether of the Old World or of the New, they are more numerous than desirable, not being noted for either their beauty or usefulness.
Class III.—Aves.[10] Birds furnish a delightful study, and their leading characteristics are easily stated. Widely as they differ, they all have a common type of structure, and are essentially alike in those particulars that distinguish them from other orders in the animal kingdom. They are all warm blooded, feathered, biped vertebrates, mostly with wings fitted for flight, and with either webbed feet for swimming, or claws for seizing, scratching, and perching.
ANATOMY OF A HEN.
Ex.—A, cranium; B, cervical vertebræ; G, furcula, or merry thought; J, sternum, or breast bone; H, cloaca, surrounded by the pelvic bones; E, caudal vertebræ, terminating in plowshare bone; D, lumbar vertebræ, or rump; C, F, dorsal vertebræ, to which the ribs are attached.
There are several points of interest in the anatomy of a bird that may be used to bring out general characteristics: (1) The long neck, with vertebræ so adjusted as to allow great freedom of movement, makes the head a convenient prehensile organ. (2) The skeleton is remarkably light. It has fewer bones than other vertebrates; the thin skull bones, the dorsal vertebræ, and bones of the feet being anchylosed.[11] They are also harder, of lighter material, and filled with air, thus having the greatest possible strength with the least weight. (3) To make respiration sufficient during rapid flight, an abundant supply of air not only inflates the lungs as in other animals, but fills little membranous sacs, or cells, distributed through the body, and extends even into the wing feathers. (4) The digestive apparatus differs materially from that of either fishes, reptiles, or mammals. The æsophagus[12] before reaching the sternum is dilated into a large sack, or crop, and serves as a first stomach, in which the food is softened, and prepared for other digestive organs. Below this is another slight enlargement, the walls of which are thicker, and secrete gastric juice. Still further down, the canal is enlarged into a third stomach, the muscular gizzard, in which the process is completed. (5) There are no teeth set in the bone sockets, as their weight would be inconvenient, but the mandibles are sheathed in a horny case, which has sharp edges, and terminates in the beak, or bill.
NESTS OF BIRDS.
Both genera and species are very numerous, but any two birds that can be selected differ less in their anatomy than some reptiles of the same order differ. The leading orders only of this class have been selected. Raptores[13] (robbers). This is a mild term when used to indicate the ferocity of most birds of prey which not only plunder but destroy. They are almost constantly committing murderous assaults on their weaker neighbors. This is their nature, and accords with their physical structure. The strong hooked bill, powerful legs, feet armed with sharp claws to seize and hold their victims, while the murderous beak is tearing off bits of flesh, are some of their chief characteristics. These murderers have representatives in nearly all countries, but as civilization advances they become less numerous.
They are usually divided into three great families: Falcons, Vultures, and Owls. The first includes all kinds of Hawks and Eagles. True falcons reveal a predatory character, not only by their general structure as described, but have a special arrangement for keeping their formidable weapons in order. The continual sharpness of their claws is necessary, and to maintain it they must be kept from coming in contact with hard substances. To make this practicable, though they are not retractile, like a cat’s claws, there not being sufficient integuments to cover them, the bird has power to elevate their points when stepping or perching on anything likely to dull them. Being very powerful and rapid flyers, falcons were in former times tamed, and trained for catching other birds and small game. Falconry, in the middle ages, was one of the principal diversions of kings and noblemen, lords and ladies, and in later times the same sport was practiced in England under the name of “hawking.” The training of the birds was a profession, and there were teachers who became proficient in it. The Eagle, king of birds, belongs to this class; he is, perhaps, inferior in activity and enterprise, but is more powerful, and his supremacy is undisputed. The Bald Eagle adorns our American flag, and is a fit emblem of national sovereignty, though there was, it is confessed, some ground for Franklin’s protest, “The bird has a bad moral character, and does not get his living honestly.” The Gypætos, or Vulture Eagle, is the largest bird of Europe, and often a terror to the peasants near the Pyrenees and Swiss Alps. Its great strength, bold, predatory habits, and impetuosity in pouncing on animals exceeding itself in size, make it more formidable than most eagles are.