i i i ee el . M ll 
52 MARGINAL MEMBRANE—THE CLAWS. 
or cut out at the joints, as in the coot, or plain, that is, straight-edged. 
(Fig. 162.) True lobation, occurring, among North American birds, only 
in the grebes, coots, and phalaropes, must be carefully distinguished from 
various 
§ 90. MarcrvaL Frinees, or processes, that birds of the lower orders 
often exhibit. Thus, if a gallinule be examined ina fresh state, it will be 
found to have a margin of membrane running along the sides of the toes, 
and the same is the case, if less evident, in a great many waders. Palmate 
birds also show it, on the free borders of 2¢ and 4¢; it is very conspicuous 
in the albatrosses, and plain enough in geese, &c. In the grouse family 
there is a remarkable development of horny substance, resembling a real 
fringe, being cut into a series of sharp teeth, or pectinations. 
§ 91. Tur Cxiaws. With certain anomalous exceptions, as in case of a 
rudimentary hind toe, every toe bears a claw. The general shape of the 
claw is remarkably constant throughout birds: variations are in degree only, 
rather than in kind. A cat’s claw represents nearly the usual shape, viz: 
compressed, arched, acute. The great talons of a bird of prey are only the 
extreme of this typical shape. Besides this general shape, the claws are 
usually dug out underneath, so that the transverse section, as well as length- 
wise outline below, is concave, and the under surface is bounded on either - 
side by a sharp edge. One of these edges, and particularly the inner edge 
of the middle claw, is somewhat dilated or expanded in a great many birds ; 
and in some it becomes changed into a perfect comb, by having a regular 
series of teeth. This pectination occurs only on the inner edge of 
the middle claw; it is beautifully shown by all the true herons (Ardeide) ; 
by the whippoorwills and nighthawks, by the frigate pelican, and, to 
a less degree, by the barn owl. It is supposed to be used for cleaning 
out lice from parts that cannot be reached by the bill; but this is open 
to question, seeing that outside the herons, it chiefly occurs among very 
short-legged birds, that cannot possibly reach many parts of the plumage 
with the toes. Besides Haptores, most perching birds are very sharp- 
clawed; the claws are more obtuse among the pigeons and Galline 
(scratchers) and still more so among most swimming birds. Obtuseness is 
generally associated with flatness, or depression; this is seen in Wilson’s 
petrel, as distinguished from all our others, and carried to the extreme in 
the grebes, where the claws resemble human nails. The deviations from 
curvature occur principally in the hind claw; this is straight or nearly so, in 
the shore lark, and some terrestrial sparrows, as the genus Plectrophanes 
(63). All the claws are straight, and prodigiously long, in some exotic 
birds of the rail tribe—the jacanas (Parra); this enables the birds to 
run lightly over the floating leaves of aquatic plants, by so much increase of 
breadth of support that they do not slump in. Claws are also variously 
carinate, suleate, etc. They are always horny. They take name from and 
are reckoned by the digits they belong to: thus, lcl. = claw of 1¢: 2el. 
= claw of 21, etc. 
es 
u-~teenn beeen 
—. 
