FLIGHTLESS BIRDS. 
556 
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 ploughshare-like bone. 
On account of the invariable absence of a keel to the 
breast-bone, this group of birds, which includes the ostrich 
and its allies, are collectively designated the Ratitai or 
Ratites—so named from the Latin term for a flat-bottomed 
boat. This group is reckoned as a subclass of equal rank 
with the Carinatce ; and by many ornithologists is subdivided 
into orders, although we shall content ourselves by arranging 
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a ratite bird. its various members in families. The existing members of 
the group, which are comparatively few in number and have 
a remarkably scattered distribution 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 different 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 consequently Carinate birds, and that 
the tinamus are their nearest living allies. 
The Ostriches. 
Family SlR UTHIONIDJE. 
The ostriches are the largest of all existing Ratites, and therefore of all living 
birds, and they are at the same time the most specialised representatives of the sub¬ 
class; this specialisation 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. 
I 11 this respect ostriches are perfectly unique among birds. While they agree with 
the majority of their allies in their short beak, ostriches are further characterised by 
the short stunted nails on the toes, the great proportionate length of the humerus 
of the rudimental wing, and the absence of after-shafts to the feathers. In the 
skeleton the furcula is wanting, the pubic bones of the pelvis unite in a symphysis 
(as they do in many reptiles but in no other birds), and the lower end of the tibia 
has no bony bridge over the extensor tendons; while there are also certain 
characteristic features in the base of the skull, into the consideration of which it 
will be unnecessary to enter. In addition to their large size and two toes, 
ostriches are characterised externally by the small and flattened head, in which 
the short beak is broad and depressed; the long, powerful, and practically naked 
neck ; the full and massive body, provided with short wings; the muscular and 
partly bare thighs; and the stout metatarsus and foot. The beak has a very wide 
gape, reaching back to the line of the eyes; and the nostrils open near the middle 
of its length. The third toe is much larger than the fourth, and both are 
furnished with soft fleshy pads on the under surface. In the immature state the 
