(A) The RATITAE are commonly characterised as Birds with no keel to the sternum; but this will not hold as a definition, since _Hesperornis_ has also that peculiarity, while such genera as _Didus_, _Stringops_, _Cnemiornis_, and _Notornis_ are nearly in the same condition. It is no one point, therefore, but the sum of many, which enables us to draw so clear a line of demarcation between this primitive group and the remainder of existing forms; nevertheless it is convenient to preserve the name unaltered, as it is well understood to what members of the class it is more especially meant to apply. The rhamphotheca, or horny sheath of the bill, instead of being simple, is composed of several more or less separate pieces, as in the Procellariidae, Tinamidae, and Steganopodes; the quadrate bone, by means of which the lower jaw is articulated to the skull, in place of two proximal knobs has only one, as in _Hesperornis_, _Ichthyornis_, and the Tinamidae; the coracoid and scapula are fused together, and meet at an obtuse, as opposed to an acute or right, angle; and the last six or seven caudal vertebrae do not coalesce into a pygostyle, or upright triangular expansion to carry the rectrices, a state of things found elsewhere in _Hesperornis_ and the Tinamidae.[16] The reduced wings preclude flight; the tail is functionless, as in the Podicipedidae and Tinamidae; the tongue is very small; the oil gland is absent; the penis is large and erectile, being comparable to that of the Anseriformes; while in the adult the feathers are evenly distributed over the whole surface, as in the Spheniscidae and Palamedeidae, no down being present. Claws are found on the pollex and index in _Struthio_ and _Rhea_, or occasionally on the third digit; in _Casuarius_, _Dromaeus_, and _Apteryx_ they occur only on the index. Ratite Birds proper are comprised in six groups, STRUTHIONES or Ostriches, RHEAE or Nandus, MEGISTANES or Cassowaries and Emeus, APTERYGES or Kiwis, DINORNITHES or Moas, and AEPYORNITHES or Rocs. {27}I. STRUTHIONES. Fam. STRUTHIONIDAE.–These birds are distinguished from all others by having only two toes–the third and fourth–the terminal phalanges of which are shortened and bear thick stunted claws, that of the outer toe being commonly absent. The whole foot, including the long scutellated metatarsus, is exceptionally stout, and the toes are padded beneath. The beak is short, broad, and depressed, with deeply split gape; the head is small, with large eyes; the neck very long; the wing- and drooping tail-feathers–the plumes of commerce–are large and soft, with broad equal vanes. The furcula and syringeal muscles are wanting, nor is there any aftershaft.