NATURAL HISTORY. 



191 



The bones of adult birds are not filled with marrow like 

 the bones of mammalia, but are hollow and filled with air, 

 and are therefore rendered very light, a bone of a goose being 

 barely half the weight of a rabbit's bone of the same size, after 

 the marrow has been extracted. In this formation, strength 

 as well as lightness is consulted, as a tubular rod is well 

 known to be very much stronger than the same quantity of 

 matter formed into a solid bar. The bones forming the wing 

 are worthy of notice for the beautiful manner in which they 

 are jointed together, and arranged so as to give great strength 

 together with lightness. In the following figure, the limbs of 

 a man and of a bird are compared, the corresponding divisions 

 of each being marked by similar letters. 



As many important characteristics are drawn from the 

 plumage, it will be necessary to give a figure, (p. 192,) exhibit- 

 ing the feathers of the different parts, together with their names : 

 A, primaries, or great quill feathers of the wing ; B, seconda- 

 ries ; c, tertials ; D, lesser coverts ; E, greater coverts ; F, winglet, 

 or bastard wing ; G, scapularies ; H, upper tail coverts ; i, under 

 tail coverts ; K, rectrices or tail-feathers. 



In the above engraving is also a figure, showing the method 

 by which birds hold on the perch while sleeping. It will be 

 seen that the great tendon A, which is connected with all the 

 toes or claws, passes over the joints in such a manner that 

 when the leg is bent, the tendon is shortened and * the claws 

 drawn together, so that the weight of the bird while perched, 

 pressing on the tendon, holds it firmly on the branch. This 



