350 COOPER'S HAWK. 



11 The proportion in which the skeleton is permeated by 

 air varies in different birds. In the Alca impennis, the Pen- 

 guins (Aptenodytes) and the Apteryx, air is not admitted into 

 any of the bones. The condition of the osseous system, 

 therefore, which all birds present at the early periods of ex- 

 istence, is here retained through life. 



"In the large Struthious Birds, which are remarkable for 

 the rapidity of their course, the thigh-bones and bones of 

 the pelvis, the vertebral column, ribs, sternum and scapular 

 arch, the cranium and lower jaw, have all air admitted into 

 their cavities or cancellous structure. In the Ostrich the 

 Jmmeri and other bones of the wings, the tibia and distal 

 bones of the legs, retain their marrow. Most birds of flight 

 have air admitted into the humerus ; the Woodcock and 

 Snipe are exceptions. The Pigeon tribe, with the exception 

 of the Crown Pigeon, have no air in the femur, which re- 

 tains its marrow. In the Owls also the femur is filled with 

 marrow; but in the Diurnal Birds of prey, as in almost 

 all other birds of flight, the femur is filled with air. In the 

 Pelican and Gannet the air enters all the bones with the 

 exception of the phalanges of the toes. In the Hornbill 

 even these are permeated by air."* 



My specimen of Cooper's Hawk is one of the largest, 

 some 20 inches long. She is sometimes scarcely more than 18 

 inches long, while the male is never more than 18, and may not 

 exceed 16 inches in length. This species, which in structure 

 and color is almost precisely like that of the Sharp-shinned 

 Hawk, being, however, unmistakably larger, makes with it, 

 and it only in this country, a strongly marked genus, the 

 Accipiter the distinctive generic points being: 1st, that the 

 feathers extend but slightly down the tarsus; 2d, that the 

 toes are long and very slender, much webbed at the base, 



* Comparative Anatomy and Physiology of Vertebrates, by Richard Owen, Vol. 1, pp. 

 213, 214. 



