In ducks and geese the beak with the exception of the anterior end is soft, and its edges are raised into lamellae, while in the Mergansers these lamellae become pointed processes supported by bony outgrowths. These lamellae act as strainers. In Parrots and Hawks, on the other hand, nearly the whole of the beak is hard. The toes and tarso-metatarsus are usually featherless and are covered either with granular structures or with well-formed scales. The toes are nearly always provided with =claws=, and these vary in correlation with the character of the beak. Claws[105] also sometimes occur on the manus. Thus _Archaeopteryx_ and some Ostriches and Rheas have claws on all three digits. Most Ostriches and Rheas, and many Anseres and birds of prey, have them on the first two digits, while the Secretary bird (_Gypogeranus_) and many fowls, ducks, and birds of prey, especially kestrels, have a claw only on the pollex. In the Cassowary, Emeu, Apteryx and some Ostriches and Rheas only the second digit is clawed. Claws should not be confounded with =spurs=, which are conical horny structures developed on bony outgrowths of the radial side of the carpus, metacarpus, or metatarsus. They occur in a number of birds, but are most commonly developed in gallinaceous birds, by which they are used for fighting. A single spur occurs on the metacarpus in _Megapodius_, in _Palamedea_, in _Parra jacana_ and in _Hoplopterus spinosus_, the Spur-winged plover. The Derbian Screamer, _Chauna derbiana_, has two metacarpal spurs, borne on the first and second metacarpals. The Spur-winged goose, _Plectropterus gambensis_, has a carpal spur borne on the radial carpal. Metatarsal spurs are quite common. The male Solitaire (_Pezophaps_) has large bony excrescences on the wrist which may, like spurs, have been sheathed in horn and used for fighting. =Teeth= do not occur in any living birds, but conical teeth imbedded in separate sockets are present in _Archaeopteryx_ and _Ichthyornis_, while in _Hesperornis_ similar teeth occur implanted in continuous grooves in the mandibles and maxillae, the premaxillae being toothless. Except that teeth are partly dermal in origin, a dermal exoskeleton is quite unrepresented in birds. ENDOSKELETON. Perhaps the most striking feature of the endoskeleton of birds is its pneumaticity. In the embryo all the bones contain marrow, but as growth proceeds this becomes replaced by air to a variable extent in different forms. In all birds some part of the skeleton is pneumatic. Many small birds and _Apteryx_ and Penguins among larger ones have air only in the skull; in Pigeons air is present in all the bones except the caudal vertebrae, the leg bones, and those of the antibrachium and manus; in Hornbills every bone contains air. [Illustration FIG. 62. THIRD CERVICAL VERTEBRA OF AN OSTRICH (_Struthio camelus_). × 1. A anterior, B posterior, C dorsal view (A and B after MIVART).