CHAPTER VL 



THE CLASSIFICATION AND THE OSTEOLOGY OF BIRDS. 



The class Aves. — Though this class contains a great 

 number of specific forms, the structural modifications which 

 they present are of comparatively little importance ; any two 

 birds which can be selected difi'ering from one another far less 

 than the extreme types of the Lacertilia, and hardly more 

 than the extreme forms of the Chelonia^ do. Hence the char- 

 acters by which the following groups are separated appear 

 almost insignificant when compared with those by which the 

 divisions of the Reptilia are indicated. 



A. The metacarpals not anchylosed together. The tail longer than the 



body. 



I. — SAURURiE. 



1. ArchceopterygidcB. 



B. The metacarpals anchylosed together. The tail considerably shortei 



than the body. 



k. The sternum dcYoid of a keel. 



II. — Ratit^. 



a. The wing with a rudimentary, or very short, humerus and 

 with not more than one ungual phalanx. 

 a. A hallux. 



2. Apterygidce (The Kiwis). 

 i8. No hallux. 



3. Dinornithidce (The Moas). 



4. Casuaridce (The Cassowaries). 



h. The wing with a long humerus and with two ungual 

 phalanges. 



a. The ischia uniting immediately beneath the sacrum, 

 and the pubes free. 



5. RheidcB (The American Ostriches). 



^ i8. The ischia free and the pubes uniting in a ventral 



symphysis. 



6. Struthionidce (The Ostriches). 

 B. The sternum provided with a keel.* 



* The keel is rudimentary in the singular Parrot Strigopa, 



