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CHAPTER XXXVII. 



Orders of Birds. 



The class Aves may be divided into the following four sub- 

 classes : — 



I. Ratit^. — Sternum raft-like, without a prominent keel 

 for the attachment of the great pectoral muscles. The barbs 

 of the feathers not united by the barbules. This sub-class 

 comprises the single order of the Oursores or Eunning Birds, 

 such as the Ostrich, Emeu, Cassowary, &c., all of which are 

 destitute of the power of flight. 



II. Carinat^. — The sternum furnished with a prominent 

 median ridge or keel, to which the muscles of flight are at- 

 tached. In this sub-class are comprised the existing orders 

 of the Natatores, Grallatorcs, Basores, Scansores, Insessores, and 

 Ra]}torcs, in all of which the power of flight is normally 

 more or less developed. 



III. Saurornithes. — The caudal vertebra numerous ; the 

 tail longer than the body, and not terminated by a plough- 

 share-bone. The metacarpals not anchylosed. This sub- 

 class includes only the single order Saururce, comprising only 

 the single Jurassic bird, the Archceopteryx macrura. 



IV. Odontornithes. — Jaws furnished with true teeth, 

 sunk in distinct sockets or in a continuous groove. Wings 

 well developed or rudimentary. This sub-class comprises 

 the two extinct orders of the Odontotormm and Odontokce, 

 both of which are confined to the Cretaceous period. 



In the foUowino- are sfiven the characters of the orders of 



