C. J. S unde vail on the Wings of Birds. 423 
cover the next feather with the outer margin. In front of 
the humerus they sometimes take on another form. 
In the Song-birds there are only two series immediately 
beneath the margin of the skin, and these are continued 
without any alteration as far as the base of the humerus. 
They are unusually soft, with separate hair-like rays, so that 
they do not present a definite outline (contour). Those in 
the outer series are small; but those of the inner one are 
very long and curved, and cover the whole under surface of 
the arm. In Corvus and Cinclus, however, they are flat and 
have a more definite form. 
Among the Coccyges, Picus major and P. martins have 
these feathers nearly as in the Song-birds, but not so long, 
and of a more definite form ; Picus viridis, like the Psittaci, 
has three series, none of which has very long feathers. 
Columba proves to be distinctly divergent; the fold of 
skin is clothed with three more widely separated series, of 
which only one occupies the margin, the second the middle, 
and the third the inner part of the fold, without any downy 
series. These feathers are rather short, rounded, and not 
curved. 
Strix has two series, of which the inner one consists of 
feathers of moderate length, soft, and but little curved; near 
the body they are larger. In Aquila , Buteo , Pernis, Astur , 
and Falco there are from four to six series below the margin, 
which occupy a considerable portion of the breadth of the 
fold, but nevertheless leave room for downy series close to 
the cubitus. The innermost are of moderate length, the 
others short; all are firm, of definite form, and but little 
curved. 
In Tetrao these feathers perfectly resemble those of the 
diurnal Birds of Prey. 
Fulica has three series, of which the inner are long and 
exceedingly soft. In Numenius, Scolopax , and Ciconia there 
are also three series, but tolerably firm and of definite form 
—the inner of moderate size, the two outer very small. 
In Anas , Linn., there are only two series of short, 
ovate, scarcely curved feathers, immediately under the 
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