174 



GENERAL ORNITHOLOGY 



treme furcation is forficate (Lat. forfex, scissors), when the depth of 

 the fork is at least equal to the length of the shortest feathers ; it 

 occurs among the birds last named, in the sjjecies of the tyrannine 

 genus Milvulus, and elsewhere. Double-forked and douhle-roimded tails 

 are not uncommon ; they result from combination of both opposite 

 gradations, in this way : The middle feathers being of a certain 

 length, the next two or three pairs progressively increasing in 

 length, and the rest successively decreasing, the tail is evidently 

 forked centrally, rounded externally, which is the double-rounded 

 form, each half of the tail being rounded ; it is shown in the genera 

 Myiadestes and Anous. Now if with middle feathers as before, the 

 next pair or two decrease in length, and then the rest increase to 

 the outermost, we have the double-forked, a common style among 

 sandpipers, as if each half of the tail were forked. But in such 

 case, the forking is slight, merel}' emargination, being little more 



Fici. 33. — Diagram of shapes of tail, adc, rouinltMl ; aec, gradate ; aic, cuneate-gradate ; ale, 

 cuneate ; ak-, double-rouuded ; /?</, square ; /;i</, emarginate ; //teog, double-emarginate ; kim, 

 forked ; Ixm, deeply forked ; khm, forticate. 



than protrusion of the middle pair of feathers in an otherwise lightly 

 forked tail ; and in the double-rounded form the gradation is seldom 

 if ever great. 



I sliould also allude to shapes of tail resulting from the relative 

 positions of the feathers. Prominent among these is the complicate 

 or folded tail of the barn-yard fowl, and others of the Phasiamda', — 

 a very familiar but not common form. It is only retained while 

 the tail is closed and cocked up, — for when it is lowered and spread 

 in flight it flattens out. The males of some of the African whydah 

 l>irds {Viduince) have remarkably large and long tails of somewhat 

 similar character. The opposite disposition of the feathers is seen 

 to some extent in crow-blackbirds (Quisccdus), where the lateral 

 feathers slant upward from the lowermost central pair, like the 

 sides of a boat from its keel ; this is the scaphoid (Gr. (TKd<fi'i], a 

 boat) or car'mate (Lat. carina, a keel) tail. The American "boat- 



