478 Mr. N. A. Vicors on the Natural Affinities 
quently within narrower limits. As we approach the Rasores, the 
order into which the plan of our inquiries now introduces us, we 
may at once notice the short wings and heavy mode of flight 
which prevail throughout the generality of the families that com- 
pose it; and we may even observe this deficiency still further 
becoming more evident, until the faculty of flying is entirely 
lost in one of the most conspicuous groups of the order. If 
we examine the internal anatomy of these birds, we shall per- 
ceive that, as far as it is conducive to the faculty of flight, it 
evinces a still more striking deficiency, than even their external 
appearance. Perhaps the most essential distinction between 
birds and the other vertebrated animals consists in the powers 
of their wings ; and the difference in their osteology is conform- 
able to this characteristic distinction. Their skeleton differs from 
all others by the peculiar formation of two important bones, 
the os furcatorius and the sternum, to which the muscles of the 
wings are attached. The first of these bones is always more or 
less robust in itself, and more or less strongly connected with the 
sternum, according as the bird possesses more or less capability 
of flight; and the latter is furnished with a projecting process or 
keel, which is also more or less elevated, according to the greater 
or less prevalence of the same capability. Now, on examining 
the Gallinaceous Birds, we find that these bones in general are 
small and feeble. The os furcatorius is attached to the sternum 
by a weak ligament; and the sternum itself is diminished in ex- 
tent by a groove on each side, which considerably affects its 
strength. In one of the families of the order, the Struthionide, 
both the os furcatorius and the projecting keel of the sternum are - 
entirely wanting, and the sternum itself, assuming the appearance 
of a simple flat buckler, exhibits the rudiments only of that struc- 
ture which is peculiar to birds. The insufficiency of these mem- 
bers to support the birds of the order before us to any height, or for 
any 
