BIKDS OF NORTH AND MIDDLE AMERICA. 13 



metasternuin usually 2-notched, rarelj^ 4-notched; biceps slip and 

 expansor secundarinruin absent; tendon oi patagiaUn irevls not ending' 

 on tendon of extensor, but continued independently and attached to 

 extensor condyle of radius. Muscle formula AXY or (very rarely) 

 AX;^ deep plantar tendons of Type VII or (in Suborder Desniodactyli 

 only) Type I;^ intestinal convolutions of Type VII or VIII. ' Hallux 

 on the same level as anterior toes, more or less distinctly (usually con- 

 spicuously) larger or stouter than lateral anterior toes, its claw usually 

 larger than that of middle anterior toe; phalanges of toes always 

 2, 3, 4, 5 from first to fourth. Primaries 10, but the outermost fre- 

 quentljr rudimentary or vestigial and quite concealed; secondaries i), 

 quinto-cubital; wing-covex'ts arranged in three distinct series, or 

 tracts, as follows: (1) Lenser core/is, a well-defined tract covering the 

 pliai idaris^ consisting of small feathers in several rows but alternating- 

 in more or less squamate or imbricate fashion; (2) middle o>»Krts, con- 

 sisting of a single row, immediately behind the last row of lesser 

 coverts, of larger feathers, most of which overlap proximally — that 

 is, have the outer web of one feather covered by the inner web of 

 the one next to it; (3) greater coverts, consisting of still larger and 

 much longer feathers with distal overlap, covering not more than the 

 basal half of the secondary remiges. Rectrices usually 12 (rarely 10 

 or 14). 



Nearly seven thousand species and subspecies,* or more ttian one-naif 

 of all existing birds, belong to the Order Passeriformes. Notwith- 

 standing this enormous number of specific forms, however, the type of 

 structure is remarkably uniform, and the group far more homogeneous 

 than the lower gi;oups of equal rank. Consequently, subdivision of 

 the Passeriformes becomes a matter of extreme difBculty, and no 

 arrangement has thus far been proposed which can be considered 

 entirely satisfactory. Indeed, it seems impossible to subdivide the 

 order, beyond a very limited extent, into lesser groups which are 

 equivalent in taxonomic rank to the families of other orders, and the 

 extent to which this may be done is a matter concerning which S3'stem- 

 atists differ widelj^ in their views. 



The latest authority on the classification of birds" allows but three 

 families of Passeriformes, while in the Catalogue of Birds in the British 

 Museum no less than forty-one are recognized. Surely between these 

 extremes there is ample room for difference of opinion and variety' of 



iGarkod, Proc. Zool. Soc. Lond., 1874, pp. 111-123, pi. 17. 



^Gaerod, Proc. Zool. Soc. Lond., 1875, pp. 339-348; Gadow, in Bronn's Thier- 

 Reichs, Vogel, 1892, p. 195; in Newton's Dictionary of Birds, pp. 615-618. 



'Gadow, Proc. Zool. Soc. Lond., 1889, pp. 303-316; in Bronn's Thier-Reichs, 

 Vogel, ed. 1891, p. 708. 



''The number recognized in the Catalogue of Birds in the British Museum is 6,480, 

 but to this number may safely be added 500 more to cover forms ignored in that 

 work and those subsequently described. 



"Hans Gadow, in Bronn's Thier-Reichs, Vogel, ed. 1893, pp. 299-302. 



