JANUARY 



149 



of fish. Ducks are swimmers. Notice their broad beaks, 

 with strainer-like teeth, the adaptation of their feet to 

 the soft mud, the boat-shaped body, and the legs well 

 placed for rowing. The ostrich, whose foot more nearly 

 approaches the human foot, is a splendid runner. 



Skeleton of Sparrow. 



Bones of Birds. 



Facts : 



Most of the bones of adult birds are hollow and filled 

 with air, Avhereas the bones of mammals are always 

 heavy, and when not solid are filled with marrow. 



This fact accounts in a great measure for the lightness 

 of the body of birds, and the length of time which a 

 diving bird can stay underneath the water. 



In the skeleton of a bird, notice the deep, thin breast 

 bone, and the " wish " or collar bone on which we fi^nd 



