CHAEACTEEISTICS OF BIKDS. 



117 



work for the thin, memhranous wing. But here the fin- 

 ger-bones are needed only for the attachment of the 

 strong feathers, and such an extension of them as we 

 have in the Bat would not conduce to strength, and there- 

 fore would be out of place. 



199. As flying requires more strength than any thing 

 else which the Bird does, the muscles of the wing are 

 larger than those in any other part of the body. It is 

 this which makes the breast so full. To accommodate 

 these large muscles, the breast-bone has a peculiar shape. 

 In man it is flat and small ; but in the Bird it is very 

 large, making a sort of convex buckler on the front part 

 of the skeleton, with a ridge or keel projecting from i't. 

 In Fig. 97 you have a front view, and in Fig. 98 a side 

 view of the breast-bone of a bird. The chief muscles 



Fig. 97. 



Fig. 98. 



that move the wings are fastened to the keel, and spread 

 over the breast-bone. In the birds that are cooked for 

 the table any one can observe that this mass of muscle or 

 meat is thickest in those birds which fly most. It is much 

 thicker in the Pigeon, for example, than it is in the com- 

 mon Fowl. In those birds which do not fly at all there 

 is little muscle on the breast, and the keel on the breast- 

 bone is absent, as you may see in the skeleton of the Os- 

 trich, Fig. 4. In such birds the bones and the muscles of 

 the lower extremities are very large, while they are com- 

 paratively small in those which are much on the wing. 



