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In birds, the claws or nails are the horny sheaths
of the terminal phalanges of the toes and fingers, generally curved, and
often sharply pointed. They are produced by a thickening of the Malpighian
layer, which forms the "nailbed" out of which the corneous cells grow.
The toes of most birds are protected by claws or flat nails, only in the
Ostrich the outer toe has no nail, or hardly any, but the often reduced
hallux is frequently unprotected. The inner side of the nail of the
third toe is often serrated like a fine comb, as in Cormorants, Herons
(including Scopus), Ibis, Dromas, Cursorius, Glareola and also in many
Nightjars. In Podicipes the distal margin of the third nail is serrated.
Nilsson, Meves, Stejneger, Collett, and Malmgren
(cf. Dresser,
B. Eur. vii. p. 189, pl. 485) described the
periodical shedding ,of the claws in Lagopus, which grow to a considerable
length during winter, the seasonal extension dropping off in spring as
do the bony fringes on the toes in the Black Grouse, Capercaillie,
and allied birds.
Claws on the tips of the fingers are much rarer.
Archaeopteryx had a well-developed hooklike claw on each of its three fingers.
In recent birds such claws are restricted, when occurring at all, to the
pollex and index, being sometimes surprisingly well developed, although
hardly functional. They occur more or less regularly on the first two fingers
in Struthio and Rhea (occasionally as embryonic traces even on the third
finger), also in Anseres
and Birds-of-Prey (for example Milvus and Cathartes). A pollex claw alone
has been found in various Anseres, in Gallus, Birds-of-Prey (especially
well developed in the Kestrel),
and individually in the Whitethroat and in the Blackbird
(Such an example of the Whitethroat is in Mr. Seebohm's collection, and
one of the Blackbird, from Syria, was described by Bonaparte (Comptes
rendus, 1856, xliii. page 412) as a new species under the name of Merula
dactyloptera.). An index claw alone occurs in Casuarius, Dromaeus,
and Apteryx.
Spurs are claws and nails in a different sense.
They are generally conical, consisting of a horny sheath which surrounds
a bony core produced by the supporting bone. Hereto belong those on the
metatarsus of many Phasianidae. Similar structures occur on the bones of
the wrist and hand, namely a long and sharp spur with strong bony core
on the radial side of the first and one on the second metacarpal bone in
Chauna derbiana; on the first metacarpal in Parra and in Hydrophasianus;
and on the radial carpal bone in Plectropterus. The large exostoses of
the size of a walnut on the wrist of the male Pezophaps were probably likewise
covered with a thickened horny layer, and were, like all these structures,
used as weapons. Young spurs can be easily grafted on various parts of
other animals.
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