BRANCH CHORD AT A; CLASS AVES : THE BIRDS 341 



opinions of various zoologists. The rank of an order in 

 this group is far lower than in most other classes. In 

 other words, the orders are very much alike and are 

 recognized mainly for the convenience in breaking up the 

 vast assemblage of species. In North America practically 

 all the ornithologists have agreed upon a scheme of 

 classification, which will therefore be adopted in this book. 

 According to this classification the eight hundred (approxi- 

 mately) known species of North American birds represent 

 seventeen orders. Certain recognized orders, for example, 

 the ostriches, are not represented naturally in North 

 America at all. As birds can usually be readily identi- 

 fied, the species being easily distinguished by general 

 external appearance, and as there are many excellent 

 book-guides to their classification, the beginning student 

 can specially well begin with them his study of systematic 

 zoology, which concerns the identification and classifica- 

 tion of species. In a later paragraph are given therefore 

 some suggestions for field and laboratory work in the 

 determination of local bird-faunae. In the following para- 

 graphs each of the American orders is briefly discu cc =ed, as 

 is also the foreign order of ostriches. 



The ostriches, cassowaries, etc. (Ratitae). The os- 

 triches, familiar to all from pictures and to some from 

 live individuals in zoological gardens and menageries, 

 or stuffed specimens in museums, together with a few 

 other similar large species, are distinguished from all 

 other birds by having the breast-bone flat instead of 

 keeled. There are about a score of species of ostriches 

 and ostrich-like birds all confined to the southern hemi- 

 sphere. In them the wings are so reduced that flight is 

 impossible, but the legs are long and strong, and they can 

 run as swiftly as a galloping horse. They are said to have 

 a stride of over twenty feet. They use their legs also as 

 weapons, kicking viciously when angered. The true 



