106 STERNUM 



that element. Her prey is of course escaping from 

 her with its best wing, though the agitation produced 

 by such a follower must of course render that wing 

 a little tremulous ; but still the motion of the prey 

 must be deducted from that of the falcon, in order to 

 get the true impetus with which the latter strikes. 

 Besides this, the bird has no resistance but that of the 

 all-elastic atmosphere, and the inertia arising from its 

 weight diminished by its motion ; and therefore a stroke 

 given with moderate velocity would have very little 

 effect upon it. But the speed of the falcon over the 

 •speed of the prey furnishes the power ; and the in- 

 strument, as already mentioned, sustains no injury on 

 account of its position, and of the communication, 

 and consequent extinction of the shock upon it ; first, 

 in the elastic part of the falcon upon which it bears 

 for support ; and, secondly, in the air, against Avhich 

 the entire body of the falcon would recoil if neces- 

 sary, as the smaller hawks may be seen to do when 

 they are flown at too heavy game. 



STERNUM. 



Far from the least remarkable part of the skeleton 

 of this model of a flier is the sternum. It will be 

 observed, on looking back to the sketch, that the 

 forks in the posterior portions of that bone are not 

 only united by bony continuations, but that only 

 a small aperture is left in the place of each. The 

 keel, or central ridge of the sternum, is also remark- 

 ably elevated, and much produced at its anterior 

 extremity, so that its outline forms a complete arch. 

 We shall afterwards have to compare the sterna of 

 different tribes with each other, and with their 

 several habits, as among the means of forming an 

 arrangement of the class, approaching at least to a 



