378 ZOOLOGY 



structures to their arms, were doomed to failure, be- 

 cause we have not a keeled sternum. We have the 

 pectoral muscles, but the greatest athlete could never 

 develop them as the bird does, having no proper surface 

 for attachment. Relatively to the size of the bird, the 

 keel is largest in those which use the wings most actively. 

 Thus the humming bird, which is incessantly in motion, 

 hovering over the flowers, has a proportionately im- 

 mense sternum when compared with the soaring alba- 

 tross. It is said that the wings of a humming bird 

 execute from six hundred to a thousand strokes a 

 minute. In groups of birds which have lost the power 

 of flight the keel of the sternum also has gone ; such are 

 the ostrich, cassowary, and apteryx. It was once 

 thought that all such birds were primitive, belonging to 

 a type prior to the evolution of flying structures ; but 

 this view is contradicted by other anatomical evidence. 

 Senses of 6. Dogs and ants are remarkable for their keen sense 



of smell. The horse, with expanded nostrils, sniffs the 

 breeze. Birds have very little sense of smell, and de- 

 pend upon their sight. The vulture does not detect the 

 odor of carrion ; it may be close at hand, and offensive 

 to the human nostril, but the bird perceives nothing. 

 Yet from the sky he detects the fallen animal by its 

 position and lack of motion. Sight suffices where the 

 most acute nostrils would fail, owing to the distance. 

 The bird's eyes are not only large, but capable of a 

 remarkable amount of accommodation; that is, adjust- 

 ment to near or far sight. It is almost as though the 

 soaring eagle possessed a telescope, which could be 

 immediately converted into a microscope as it swooped 

 upon its prey. The human eye is incapable of such 

 feats, though possessing the same powers to a limited 

 extent ; that we see smaller and more distant things than 



