BIRDS OF NORTH AND MIDDLE AMERICA. * 13 



metasternum usually 2-notched, rarely i- notched; bicep.s slip and 

 expansor secundarioruni absent; tendon oi j)(ftagialls hrevis not ending 

 on tendon of extensor, but continued independenth' and attached to 

 extensor condyle of radius. Muscle formula AXY or (ver\' rarely) 

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

 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, -i, 5 from lirst to fourth. Primaries 10, but the outermost fre- 

 quently rudimentar}' or vestigial and (juite concealed; secondaries 9, 

 quinto-cubital; wing-coverts arranged in three distinct series, or 

 tracts, as follows: (1) JOesse?' coverU^ a well-defined tract covering the 

 jil'icd (ihn'ix^ consisting of small feathers in several rows but alternating 

 in more or less squamate or im])ricate fashion; (2) middle coi'i^rt.s, con- 

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

 coverts, of larger feathers, most of which overlap proximallv — 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. Kectrices usually 12 (rarely 10 

 or 11). 



Nearly seven thousand species and subspecies,* or more than 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 groups of equal rank. Consequently, subdivision of 

 the Passeriformes becomes a matter of extreme difficulty, and no 

 arrangement has thus far been proposed which can be considered 

 entirel}' satisfactor}-. Indeed, it seems impossible to subdivide the 

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

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

 extent to which this ma}' be done is a matter concerning which system- 

 atists difier wideh' 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 variet}" of 



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



-Garrod, Proc. Zool. Soc. Lond., 1875, pp. 339-348; Gadow, in Bronn'n Thier- 

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



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

 Yogel, 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 descril)ed. 



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



