The skull is short and robust; while the neck is abnormally developed, with extra vertebrae, in the Swans, and is usually long, though less so in the Sea-Ducks; in the _Merginae_ and some _Fuligulinae_ the customary posterior notches in the sternum are converted into two complete fenestrae or apertures. The bill is almost entirely covered with a soft sensitive membrane, ending in a horny process termed the nail, the skin being warty in _Anseranas_ and _Chen rossi_; _Cereopsis_ has a large tumid cere; both sexes of _Cygnus melanocoryphus_ and _C. olor_ have a knob at the base of the culmen, as have the males of _Plectropterus_, _Tadorna cornuta_, and the domesticated form of _Cycnopsis cycnoïdes_; the same sex of _Somateria spectabilis_ has the posterior portion of the maxilla spread into a disk; _Oedemia_ has it considerably swollen even in the female; _Cairina_ and _Plectropterus_ have caruncles on the forehead; _Sarcidiornis_ has a fleshy comb at the proximal extremity of the beak in the male; while _Biziura_ has a dependent flap on the chin, and a small subgular pouch. The bill is usually broad and depressed, and may be sub-conical, as in many Geese; spatulate, as in _Spatula_ and _Malacorhynchus_; or somewhat less dilated, as in _Chaulelasmus_, and so forth. There is a distinct hook at the tip in _Mergus_, _Dendrocycna_, and _Aex_; the culmen is concave in _Marmaronetta_ and _Stictonetta_; the nail is bent inwards in the latter and _Erismatura_, while the maxilla may overlap the mandible, or the covering membrane may even hang over the latter, as in _Malacorhynchus_, _Hymenolaemus_, and to a less extent in _Elasmonetta_ and _Nesonetta_. The length is very variable, but the thin elongated "sawbill" of _Mergus_, with its serrated edges, is especially remarkable. Most characteristic of the Family is the presence of highly-developed lamellae or transverse tooth-like processes on both maxilla and mandible, which are visible when {112}the jaws are closed in many cases, and are comparable to the similar formations in _Prion_ (Procellariidae) and the Phoenicopteridae. They act no doubt as a sifting apparatus, but may assist in nipping off herbage and gripping fish, the piscivorous Mergansers having them directed backwards. The metatarsus is normally short or moderate, though occasionally long, as in _Plectropterus_ and _Dendrocycna_; it may be stout and roundish, as in _Anser_, or laterally compressed, as in _Fuligula_; and is usually reticulated with transverse scutellae in front, though wholly reticulated in the Cygninae, Anserinae, and _Dendrocycna_. The anterior toes are fully webbed, _Anseranas_ and _Cereopsis_ alone having the foot semi-palmated; the hallux is short and elevated–except in the former species, where it is long and incumbent–and possesses a broad membranous lobe in the Merginae, Merganettinae, Erismaturinae, and Fuligulinae, while a very narrow membrane may be observed in the Anatinae and Chenonettinae. The claws are as a rule