478 Mr. N. A. Vigors on the Natural Affinities 



quently within narrower limits. As we approach the Rasoresy 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 Struthionidce, 

 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 strucr 

 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 



