458 



NATURAL HISTORY OF BIRDS. 



ORDER XVIII. PASSERES. 



This order comprises in round numbers say six thousand species, or more than half 

 the number of all the known birds. In the foregoing pages of this volume, conse- 

 quently, we have dealt with a less number of species than this order alone contains. 

 The great majority of the Passerine species, however, are so closely allied that it is 

 only in catalogues and nominal lists that they take up the greatest space ; while here, 

 where we have to consider the forms according to their biological and morphological 

 features, the present order will receive a treatment commensurate with the importance 

 of the group in these respects, but not with the number of the species. 



There seems to be no single character by which the Passeres, as here and most 

 commonly defined, can be separated from all the rest of the birds. Hence the only 

 characteristic which can be formulated in a few words is that they possess a number 

 of characters which are not combined in the same Avay in any bird included in the 

 foregoing orders. It is especially among the Picarians that we find forms which 

 approach the Passeres very closely in some of their characters, while, on the other 

 hand, a few generalized Passerine birds have retained some ancestral peculiarities 

 which link them to the groups below. 



We have seen that aacrithognathism is no exclusive character : in most Passeres the 



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manubrial process of the sternum is bifurcate, but it is so in some higher or passeri- 



form Picarians ; the hind 

 margin of the breastbone 

 has mostly only two notch- 

 es, but in a few has four, 

 and in some Picarire has 

 also only two ; the Passeres 

 have casca and no tuft to 

 the oil-gland, but many Pi- 

 carians are similarly charac- 

 terized ; the Passeres have 

 a peculiarly specialized ar- 

 rangement of the wing-cov- 



O O 



erts, a feature already noted 

 on a previous page when we 

 said that Avoodpeckers and 

 some allied forms present 

 the same kind of specializa- 

 tion. The schizopelmous arrangement of the deep plantar tendons would have been 

 an excellent distinction but for the fact that the hoopoes are also schizopelmous, while 

 the Eurylaimidae, which are otherwise true Passeres, have the flexor hallucis attached 

 to the perforans digitorum by means of a strong vinculum, making them desmopelmous. 

 Another myological feature which is peculiar to the Passeres inasmuch as it does not 

 occur in other birds, though not in all Passeres, is the distal insertion of the tensor 

 patagii brevis, a muscle which has already been mentioned under the head of the 

 Micropodoideae. Being obliged to treat of this character more in full, we shall try 

 to use Professor Garrod's own words whenever possible. 





FIG. 228. Diagram of the elbow-muscles in (A) Icterus and (B) Menura; 

 muscles with longitudinal, tendons with transverse, lines ; b, biceps ; emrl, 

 extensor metacarpi radialis longus ; h, luunerus ; s, shoulder ; sr, second- 

 ary remiges ; t, triceps ; tpb, tensor patagii brevis ; tpl, tensor patagii 

 longus. 



