272 THE ANATOMY OF VEBTEBEATED ANIMALS. 



CHAPTER VI. 



THE CLASSIFICATION AND THE OSTEOLOGY OP BIRDS. 



The class Aves — Thougli this class contains a great 

 number of specific forms, the strnctural modifications whieh 

 they present are of comparatively little importance ; any 

 two birds which can be selected dilTering from one another 

 far less than the extreme types of the Lacertilia, and hardly 

 more than the extreme f orm.s of the Chelonia, do. Hence the 

 characters 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 ankylosed together. The tail longer than 



the body. 



I. — Saurur.=e. 



1. ArcliaopterygidcB. 



B. The metacarpals ankylosed together. The tail considerably shorter 



than the bod}'. 



A. The sternum devoid of a keel. 



II. — RaTITjE. 



a. The winp; with a rudimentarj', or very short, humerus 



and with not more than one ungual phalanx. 

 a, A hallux. 



2. Apterygidcs (The Kiwis). 

 P. No hallux. 



3. Dlnornithidx (The Moas). 



4. Ca^varidoi (The Cassowaries). 



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



phalanges. 



a. The ischia uniting immediately beneath the 

 sacrum, and the pubes free, 

 ."i. RlieidcB (The American Ostriches). 

 /3. The ischia free and the pubes uniting in a 

 ventral symphysis. 

 6. Struthionidoe (The Ostriches). 

 B. The sternum provided with a keel.* 



The keel is rudimentary in the singular Parrot Scriffopn. 



