138. =Membrane= (_Palama_). A skin either soft or covered with
scales or feathers connecting two adjacent toes together at the
base, and sometimes extending to or beyond their tips. The foot so
constructed is called
139. =Palmate= (_palmatus_) when the anterior toes only are so
connected and
141. =Oared= (_Steganopus_), where all the toes, including the
hinder, are so connected in the cormorants, etc. The feet may be
half, or semipalmate; entirely or totipalmate.
NOTE. In the usual arrangement of the toes, of three before and one
behind, the hinder corresponds to the great toe of man, or the first;
the inner anterior is the second; the middle is the third; and the outer
is the fourth. When the toes are in pairs or two before and two behind,
it is the outer or fourth toe that is turned backwards, as is the
woodpeckers. In the Trogons, however, the inner toe is reversed. With
scarcely an exception in birds, the hinder or first toe has two joints;
the inner (2d) has three; the middle (3d) has four; and the outer (4th)
has five, or a formula of 2.3.4.5. In the typical _Caprimulgidæ_ the
outer toe has only four phalanges the formula being 2.3.4.4. Finally,
in some _Cypselidæ_ (_Cypselus_ and _Panytila_), we have the middle and
outer toes with three joints only each, the formula being 2.3.3.3. When
there are but three toes, the hinder or first is wanting; the ostrich
(_Struthio_) has but two toes, lacking the first and second.
H. The Outer Covering (_Indumentum_).
142. =Outer covering= (_Indumentum_; _Ptilosis_). The exterior of the
bird in detail.