BIRDS OF NORTH AND MIDDLE AMERICA. 3 



(4) Articulation of the lower jaw with u .separate bone {os qxad- 

 ratum), which again articulates with the skull. 



(5) Absence of a diaphragm. 

 They differ from Reptiles in — 



(1) Possession of feathers. 



(2) Complete circulation of warm blood. (In this. Birds agree with 

 Mammals.) 



The fact that Reptiles, as well as Birds, la}^ eggs, and that the nidi- 

 tication of some members of the two Classes is practically identical (e. 

 g., the reptilian Crocodilia and avian Megapodid* (a group of Peri- 

 steropode Gallinfe), is too well known to require more than mere men- 

 tion here; but the mammalian Monotremata also lay eggs, while 

 furthermore one of the latter {OnuthorJiynckus^ the duck mole of 

 Australia), possesses a ver}- duck-like beak. 



KEY TO THE Sl'BCLASSES OF AVES. 



(I. Metacarpals separate, the first finger with 2, the second and third each witli 8, 

 digits; caudal vertebneahout 21, not terminating in a pygostyle; primaries not 

 more than 7; rectrices attached in pairs (about 12), each to a caudal vertebra. 



Subclass Saururae.' 



a<i. Metacarpals fused; caudal vertebne not more than 13, of which about half are 



usually fused into a pygostyle;^ primaries 10-16;'^ rectrices not attached to 



separate vertebrte Subclass Ornithurffi.* 



The Subclass Saururte (i\.rchteornitlies of Gadow) is represented 

 only by the extinct (Upper Jurassic) ArcJueopteryx,' all existing birds 

 belonging to the Ornithura' (Neornithes of Gadow). 



The construction of a ''key" to the orders and other supergeneric 

 groups of the Subclass Ornithurte, which shall serve for ready identi- 

 fication and at the same time express the mutual relationships and com- 

 paratiA'e taxonomic value of the different groups, has been found a 

 most difficult task. When the highest authorities disagree, as they 



^Sauriurx Haeckel, Gen. Morph. Org. 1866, — . — Saururx Huxley, Proc. Zool. Soc. 

 Lond., 1867, 418; Carus, Handb. Zool., i, 1868,367; Newton, Enc. Brit., xviii, 1884, 

 44; Ste.j.\eger, Stand. Nat. Hist., iv, 1885, 21; Cope, Am. Nat., xxiii, 1889, 869; 

 Beddard, Struct, and Classif. Birds, 1898, 529. — OrttilJiopappi Ste.tneger, Stand. Nat. 

 Hist., iv, 1885, 21; Cope, Am. Nat. xxiii, 1889, 869. — ArcJioniithes Fuerbrixger, 

 Unters. Morph. Syst.Vog., ii, 1888, 1565. — Archieornithes Gat>ow, Bronn'sThier-Reichs 

 Vog., ii, 1893, 86, 299. — Archseopterygiformes and Archxopteryges Fcerbringer, Unters. 

 Morph. Syst. Vog., ii, 1888, 1565. — Saurornithes Beddard, Struct, and Classif. Birds, 

 1898, 529. 



'•'Exceptions to the presence of a pygostyle are the Division Ratitse, Orders Cryptu- 

 riformes and Sphenisciformes, and Suborder Podicipedes. 



■^Sometimes the tenth (outermost) primary is rudimentary, even to such a degree 

 that it is apparently absent. * 



^Ornithune Haeckel, Gen. Morph. Org., 1866, — ; Beddard, Struct, and Classif. 

 Birds, 1898, IQ7 .—Xeornithes Gadow, Bronn's Thier-Reichs, Vog., ii, 1893, 90, 299; 

 Classif., Vertebr. 1898, xiv, 30. 



