FLIGHTLESS BIRDS. 555 



evident they were derived from flying-birds quite independently of the modern 

 flightless birds. 



Eocene Flightless As they may possibly have some connection with the Stereor- 

 Birds. nithes, although it is almost as probable they may form a group by 

 themselves, it may be convenient to mention here certain giant extinct birds from 

 the Lower, Eocene of France, England, and the United States, which constitute the 

 family Gastornithidce. All have a bony bridge at the lower end of the tibia, 

 while in the European Gastornis the component bones of the skull remained 

 separate throughout life, and it is possible that there may have been a large tooth 

 on each side of the upper jaw, while the symphysis of the lower mandible was 

 short. In North America the group is represented by Diatryma. 



THE FLIGHTLESS OR OSTRICH-LIKE BIRDS. 

 SUBCLASS Ratitse. 



With the exception of certain specially modified species like the dodo, in 

 which the power of flight has been lost, the existing birds hitherto treated are 

 characterised by the circumstance that the breast-bone is provided with a strong 

 vertical median keel, to afford support for the muscles necessary for flight, while 

 both the scapula and metacoracoid are separate elongated bones, forming an acute 

 or right angle at their junction. On account of this general presence of a keel to 

 the breast-bone, the foregoing orders are brigaded together into a single assemblage 

 or subclass, known as the Carinatce, which may be anglicised into Carinates. As a 

 rule, the Carinates possess to a greater or less degree the power of flight ; and 

 they are further generally characterised by the circumstance that in the pelvis the 

 bones known as the ilium and ischium are united at their outer extremities so as 

 to enclose a foramen l ; while the head of the quadrate bone, by which the lower 

 jaw articulates with the skull, is double ; and in the palate the vomer (except in 

 the tinamus) is not fused with the neighbouring bones, or interposed between them 

 and the rostrum of the sphenoid. On the other hand, in the birds now to be con- 

 sidered the breast-bone is invariably devoid of a keel, while the metacoracoid is short 

 and united with the scapula, and the two bones form a very obtuse angle at their 

 junction 2 ; moreover, the furcula is incomplete, so that its two branches remain quite 

 separate. All these birds further agree in having their wings greatly reduced, so as 

 to be utterly useless for flight. They are also characterised by the extremities of the 

 ilium and ischium (except in very old individuals of the rheas and emeus) remaining 

 distinct 3 ; and likewise by the single head of the quadrate bone, as they are by the 

 vomer, which is broad behind, being interposed between the other bones of the palate 

 and the rostrum of the sphenoid, and also frequently fused with some of them. 

 Other features of the group are the absence of an oil-gland, and of any marked 

 distinction between feathered and unfeathered areas on the skin ; while the hook- 



1 This circular foramen or vacuity is shown in the pelvis of the skeleton of the parrot figured on p. 292 of 

 Vol. III. 



- This arrangement is shown in the figure on p. 294 of Vol. III., which is taken, by the way, from an aberrant 

 Carinate. 



a See figure in Vol. III. p. 290. 



