THE OSTRICHES 2327 



tiou;* 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 characterized by the extremities of 

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

 remaining distinct ;f 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-like or uncinate processes of the ribs are never more than three in number, 

 and are often rudimental, or even absent. In addition to the agreement in the 

 structure of the skull, they resemble the tinamus in that the terminal vertebrae of 

 the tail are not united to form a plowshare-like bone. 



On account of the invariable absence of a keel to the 

 breastbone, this group of birds, which includes the 

 ostrich and its allies, are collectively designated the 

 Ratitce or Ratites so named from the L,atin term for a 

 flat-bottomed boat. This group is reckoned as a sub- 

 class of equal rank with the Carinatce, and by many 

 KEELLESS BREASTBONE OF ornithologists is subdivided into orders, although we 

 A RATITE BIRO. shall content ourselves by arranging its various mem- 



bers in families. The existing members of the group, 



which are comparatively few in number and have a remarkably scattered distribu- 

 tion on the surface of the globe, are widely different from one another in structure, 

 and include the largest of all birds, while none of them are very small. Very dif- 

 ferent views have been entertained as to the relationship of these Ratite birds to the 

 Carinates; it having at one time been supposed that the former might represent the 

 ancestral stock from which the latter was derived. There is, however, now a pretty 

 general consensus of opinion that the Ratites are derived from flying, and con- 

 sequently Carinate birds, and that the tinamus are their nearest living allies. 



THE OSTRICHES 







Family STRUTHIONID^E 



The ostriches are the largest of all existing Ratites, and therefore of all living 

 birds, and they are at the same time the most specialized representatives of the sub- 

 class; this specialization showing itself in the reduction of the number of toes to 

 two, owing to the absence not only of the first or hind-toe, but likewise of the 

 .second. In this respect ostriches are perfectly unique among birds. While they 

 agree with the majority of their allies in their short beak, ostriches are further char- 



*This arrangement is shown in the figure on p. 1466 of Vol. III., which is taken, by the way, from an 

 aberrant Carinate. 



fSee figure in Vol., III. p. 1462. 



