848 STERNUM OF THE HOOPOE. 



the surface to which its origin is attached, in pro- 

 portion to the grand pectoral, than birds which have 

 a descent in their rushing motions. 



The different style and direction of the flight are 

 not, however, the only circumstances to which the 

 muscles have to be accommodated. The bird requires 

 to be able to make its way through the air the 

 more easily the greater length of time that it spends 

 on the wing, and this easiness of the motion has 

 reference to the respiratory and circulating systems 

 of the bird, as well as to the fatiguing or not fatiguing 

 of the muscles. Now, if we may judge from the 

 analogies, which, as far as we can trace them in all 

 living nature, agree, we must conclude, that, up to a 

 certain rate of speed, the short muscle, moving the 

 comparatively light member, is that which can con- 

 tinue longest in action without fatigue to the muscles, 

 or derangement to any part of the system ; but that, 

 beyond a certain rate of motion, the long muscle is 

 the best for speed, though the continuation of its 

 action is shorter than that of the other. We find 

 this in the limbs of the mammalia, and in the feet of 

 birds, whether used in walking or in swimming, as 

 well as the wing, and the principle is one of considerable 

 importance in the economical use of animal power. 



The hoopoe, which we shall select as a specimen of 

 anisodactylic feet, with the habit differing the uiost 

 from that of the swimming birds, lias the tarsi much 

 longer and stronger, and instead of walking with 

 difficulty on the ground, it walks with a sort of strut, 

 as if it had more power there than what is absolutely 

 necessary for moving it along. The following figures 

 represent the sternal apparatus of the natural size. 



It will be seen that the general form of the sternum 

 is nearly the same as that of the humming-bird, but 



