The Anseres of Linnaeus (Natatores of Illiger) were a very large group, comprising almost all web-footed birds ; but the term Anseres as used by ornithologists at the present day is restricted to the Ducks, Geese, and Swans, which form a well-marked order without any near relations.
In this order the three anterior toes are united by webs extending, except in one Australian genus, Anseranas, to the ends of the digits; the hind toe is always present, but is short and articulated to the tarsus higher up than the other toes. The bill is more or less depressed and flattened, except in the Merginae, and is covered with a soft membrane, except on the dertrum or nail, which forms the tip of the upper mandible; both mandibles are fringed inside the tomiae, or edges, with lamellae, which are variously developed in different genera.
The skull is desmognathous and holorhinal; basipterygoid pro cesses are represented by oval facets, articulating with the pterygoids close to the anterior extremity of the latter, as in Gallinae. The angle or posterior extremity of the lower jaw is produced backwards beyond the articulation with the quadrate, and is curved upwards. Nostrils pervious. Furcula U-shaped ; posterior border of sternum with a notch, represented in some genera by a foramen, on each side of the keel. Two carotids; caeca large ; oil-gland tufted. Wing aquincubital; primaries 11; aftershaft to body-feathers rudimentary or wanting; no bare spaces on the neck. Ambiens muscle present, as also the femoro-caudal, accessory femoro-caudal (very large), and the semitendinosus; accessory semitendinosus absent, as in most swimming-birds. The flexor longus hallucis sends off a slip to the hallux, and then fuses with the flexor perforans digitorum, which supplies the three anterior digits. Tongue large and fleshy, denticulated laterally to correspond with the lamellae of the mandibles. Males with a large spiral intromittent organ. All the species are monogamous, and the majority build nests of grass or rushes on the ground, a few on trees or in holes. In cold climates the female lines her nest with her own down, and surrounds with the same the eggs, which are numerous, and white, cream-coloured, buff, or pale green in colour; but in warmer countries, as in India, less precaution for retention of heat is necessary, and the downy lining is imperfect or wanting. The young are hatched covered with down, and able to run or swim at once. In moulting, most, if not all, of the members of this order shed all their quill-feathers at once, and are consequently, for a time, unable to fly. There is but a single family.