AVES

(Lat. avis, a bird.) The name of a cla of warm-blooded vertebrated animals, characterised by a double circulation and respiration, oviparous generation, a covering of feathers, and by their anterior extremities being organised for flight. The posterior extremities present five principal modifications, affording characters which distinguish five primary orders. In the first order the foot (a fig.) has three toes before and one behind, all armed with long, strong, crooked, and more or le retractile talons, adapted to seize and lacerate a living prey; this structure is a ociated with a strong, curved, sharp-edged and sharp-pointed beak, often armed with a lateral tooth; a very muscular body, and capability of rapid and long-continued flight. The order is termed Raptores or Accipitres. The second type of foot presents three toes before and one behind, and placed on the same level; slender, flexible, of moderate length, and provided with long, pointed, and slightly curved claws. The two external toes are united by a very short membrane. A foot so constructed (b fig.) is especially adapted for the delicate operations of nest building, and for grasping and perching among the slender branches of trees; hence the order so characterised has been termed In se ores, and, from including the smaller tribes of birds, Pa eres. In the third type of foot (c fig.) the hinder toe is raised above the level of the three anterior ones; this deteriorates the power of perching; but the other toes are strong, straight, and terminated by robust obtuse claws, adapted for scratching up the soil, and for running along the ground; the legs are for this purpose very strong and muscular, and the order so characterised is termed Rasores, or Gallinae. The modification by which birds are enabled to wade and seek their food in water along the margins of rivers, lakes, and estuaries, is gained simply by elongating the bones of the leg (tibia and metatarsus), which are covered with a naked scaly skin. The three anterior toes are sometimes very long and slender, as in the Parra jacana, by^ which the bird can support itself upon the broad floating leaves of aquatic plants; sometimes they are of moderate length. The hind toe is elevated, short, and sometimes wanting (d fig.). The order of birds characterised by this form of leg and foot is termed Grallatores, from the resemblance of the pos  [s. 124]