BIRDS 



65 



alone would seem to necessitate many and varied instru- 

 ments : yet all this is made possible, and chiefly executed, by 

 one small portion of the bird — its bill or beak." ^ 



While the size and shape of the bill varies greatly in differ- 

 ent kinds of birds, it always consists of two parts (mandibles) 

 (Fig. 46), which correspond in position to the upper and 

 lower jaws of man. When 

 the bill is opened, a careful ex- 

 amination shows that a bird 

 has no teeth. Some of the 

 birds that lived ages ago, 

 however, had well-developed 

 teeth in their jaws, as is well 

 shown in (Fig. 47) which is a 

 picture of a bird skeleton re- 

 stored from bones found in 

 the rocks of western Kansas. 



Near the base of the bill 

 on either side, one can usually 

 see an opening ; these open- 

 ings are the nostrils. On the 

 sides of the head are the two 

 eyes, and since they bulge out 

 somewhat, the bird is afforded a wide range of vision. If 

 the feathers below and behind the eye are pushed aside, an 

 opening into the ear may be seen ; this may be made out easily 

 in the head of a chicken. 



51. Wings. — In Figure 48 are shown the bones that com- 

 pose the wing of an ostrich and the arm of a man, and on com- 

 paring the two one sees a striking resemblance. In both, 

 the upper arm has a single bone, while in the forearm there 



Fig. 47. — Skeleton of a fossil bird. 



'Beebe, "The Bird. 



