THE STRUCTURE AND ACTIVITIES OF MAMMALS 411 



noted (p. 349) that the study of birds is often interfered with 

 by the leaves of trees which hide them. As a remedy it was 



upper jaw bone 

 lower jaw bone 



collar bone 



knee cap 



vertebrae 



shoulder blade 

 breast bone 



wrist bones 



Fig. 280. — Skeleton of man. (From Peabody and Hunt.) 



suggested that the call notes and songs of birds should be learned, 

 since we could thus recognize the birds, even if we could not see 



