BIRDS OF NOETH AND MIDDLE AMERICA. d 



(4) Articulation of the lower jaw with a separate bone {ox quad- 

 Tdtum), 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, lay eggs, and that the nidi- 

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

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

 steropode Gallinse), 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 {Ornitliorhynclms^ the duck mole of 

 Australia), possesses a very duck-like beak. 



KEY TO THE SUBCLASSES OF AVES. 



<'. Metacarpals separate, the first finger with 2, the second and third each with 3, 

 digits; caudal vertebrje about 21, not terminating in a pygostyle; primaries not 

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



Subclass SaurursB.^ 



an. Metacarpals fused; caudal verjebrse not more than 13, of which about half are 



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



separate vertebrae '. Subclass Ornithuree.' 



The Subclass SaururtB (Archgeornithes of Gadow) is represented 

 only by the extinct (Upper Jurassic) ArcJimopteryx; all existing birds 

 belonging to the Ornithurse (Neornithes of Gadow). 



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

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

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

 parative taxonomic value of the different groups, has been found a 

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



^Sauriuras Haeckbl, Gen. Morph. Org. 1866, — . — Saururw Huxley, Proc. Zool. Soc. 

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

 44; Stejneqbr, Stand. Nat. Hist, iv, 1885, 21; Cope, Am. Nat, xxiii, 1889, 869; 

 Beddaed, Struct, and Classif. Birds, 1898, 529. — Ondthopappi Stejnegee, Stand. Nat. 

 Hist., iv, 1885, 21; Cope, Am. Nat. xxiii, 1889, 869. — Archornithes Fuerbeixger, 

 Unters. Morph. Syat.Vog., ii, 1888, 1565. — Archxornithes Gadov/, Bronn'sThier-Eeichs 

 Vog., ii, 1893, 86, 299. — Archseopterygiformes and Archasopteryges Fueebeingee, Unters. 

 Morph. Syst. Vog., ii, 1888, Ib^b.—Saurorniihes Beddaed, Struct, and Classif. Birds, 

 1898, 529. 



* Exceptions to the presence of a pygostyle are the Division Ratitje, Orders Oryptu- 

 riformes and Sphenisciformes, and Suborder Podicipedes. 



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

 that it is apparently absent." 



^Ornithurie Habckel, Gen. Morph. Org., 1866, — ; Beddaed, Struct, and Classif. 

 Birds, 1898, 167 .—Neornithes Gadow, Bronn's Thier-Reiohs, Vog., ii, 1893, 90, 299; 

 Classif., Vertebr. 1898, xiv, 30. 



