THE FLIGHT OF BIRDS 299 



at this joint a good deal of rotatory movement is possible, a 

 matter of great importance in adjusting the wing to advantageous 

 positions for flight. The two usual bones (radius and ulna) are 

 found in the forearm, but no twisting movement is possible 

 at the elbow, as in ourselves. In this case it would detract from 

 firmness and therefore be a disadvantage. A certain amount of 

 fusion has taken place in the hand; here again, no doubt, in the 

 interests of firmness. For though two of the little wrist-bones 

 (radiale and ulnare) are separate, the remainder have united with 

 the elements making up the palm-region (metacarpus). This 

 bears the three digits, of which the middle one is the largest 

 and most important. 



The breastbone (sternum) of a flying bird is exceedingly 

 large, and a vertical plate or keel projects from its under sur- 

 face, giving additional surface for the attachment of the great 

 muscles of flight which make up the flesh of the breast. 



Chief Muscles of Flight (fig. 834). So far we have been 

 concerned with the supporting framework, and, as in other cases, 

 the actual movements are brought about by the shortening or 

 contraction of muscles. Of these the largest and most important 

 are situated entirely or partly in the trunk, and are attached to 

 the bones they move by means of inelastic cords or tendons. 

 There are, however, a large number of smaller muscles situated 

 entirely in the wing itself. And besides tendons there are other 

 fibrous bands known as ligaments, which connect bones, &c., 

 together. The advantageous situation of the large muscles is 

 commented on very graphically in the following passage taken 

 from Headley (Structure and Life of Birds): " It is a strange 

 thing that in these days when it is boasted that machines can 

 be made to do most things that a man can do, that sailors should 

 still have to run up the rigging, be the weather foul or fair, and 

 straddle across the yards, in order to furl or set the sails. It 

 would not seem to be beyond human ingenuity to devise 

 machinery by the aid of which this work should be managed 

 from the deck. Some progress towards this has, I believe, been 

 made. In the bird we find such machinery brought to great 

 perfection. Instead of men we have muscles, and by the machin- 

 ery of tendons and ligaments these muscles, situated on or near 

 the body, are able to spead the wings and regulate their utmost 

 extremities. It is all-important that it should be so. All the 



