122 



NATURAL HISTOKY. 



enables the Eagle, and other birds also, to look directly 

 at the sun. The sense of smell is very acute in all birds 

 in which it can be of service in searching for food, as, 

 for example, in those that live on carrion. While all 

 birds have ears, there is only one kind, the Owl tribe, 

 that has any external ear. In all others there is merely 

 an opening to the passage leading to the internal appa- 

 ratus of hearing, and even this is concealed among the 

 feathers of the head. 



208. Birds are digitigrade, 92. You can see this to 

 be true in the case of the Ostrich, Fig. 4, if, comparing 

 the bones of the leg with the same bones in man, Fig. 1 7 

 you begin at the thigh-bone and go downward. In Fig. 

 101 you have the bones of a bird's leg, a being the thigh- 



Fig. 101. Fig. 102. Fig. 103. 



bone, b the bones of the leg proper, c the heel-bone, long 

 and extending upward, and d the bones of the foot. In 

 Fig. 102 is the outline of the leg of a man, with letters 

 to correspond with those of Fig. 101, that you may read- 

 ily make the comparison. In Fig. 103 you have the 

 perching apparatus of birds represented, and you can 

 see how it is that they can sleep on their perches with- 

 out falling oif. There is, you observe, a large muscle in 

 front of the thigh-bone ; from this a long tendon or cord, 

 A, extends down the leg, and in the foot it divides into 

 branches, which go to all the toes. When the muscle 

 pulls on this the toes will all be bent, as every body 



