BIRDS. 



347 



SUB-ORDER 2. IMPENNES. 



Aquatic birds with short, paddle-like wings used only for swimming. 

 Pterylae and apteria not differentiated ; no differentiated remiges ; dorsal 

 vertebrae opisthoccelous and movable; 

 synsacrum poorly developed ; skull 

 schizognathous ; uncinate processes 

 not anchylosed to ribs ; pollex absent ; 

 pubis not united to ischium behind ; 

 four toes ; feet plantigrade. The pen- 

 guins, of which there are several gen- 

 era {Aptenodytes, Spheniscus, etc.) are 

 confined to the colder portions of the 

 southern hemisphere. They are flight- 

 less, but use their wings, which are 

 covered with scale-like feathers, as 

 paddles in swimming. They feed 

 upon fish and shell-fish, and make 

 their nests upon uninhabited islands. 

 Palceeudyptes occurs in the eocene of 

 New Zealand. 



FIG. 339. Penguin, Aptenodytes 

 longirostris, after Liitken. 



SUB-ORDER 3. EUORNITHES. 



Non-dromaeognathous birds with 

 (usually) saddle-shaped centra to the 

 dorsal vertebrae ; distal caudal verte- 

 brae united to a pygostyle ; quadrate with two articular facets ; ilium and 

 ischium united behind, enclosing an iliosciatic foramen ; pollex free ; 

 pterylas and apteria differentiated. 



To this sub-order belong the great majority of living birds, over twelve 

 thousand in number. They are usually sub-divided into a number of groups 

 commonly regarded as ' orders,' but which are only of family rank, the so- 

 called families being equivalent to genera in other groups of vertebrates. 

 Reference must be made to special works on ornithology for details, as 

 space will only allow mention of families here, with such features as will 

 allow of correlation of other works with the system here adopted. 



SECTION I. DESMOGNATH/E. Birds with desmognathous pala- 

 tine structure (p. 334). The STEGANOPODES are strong flying, web-footed 

 birds, in which all four toes are directed forwards, while basipterygoid 

 processes are lacking. The tropic birds (Phaethon) have all the toes con- 

 nected by a web, while in the frigate birds (Fregatd) the web is scarcely 

 developed. The pelicans (Pelecanus}, with twenty-four tail-feathers, are 

 characterized by the enormous pouch connected with the lower jaw. The 

 gannets (Sula}, the cormorants (Phalacrocorax}, and the darters (Anhinga^ 

 also belong here. The CHENOMORPH.E have three toes directed forwards, 



