THE TURKEY 83 



rapidly. Such opposite actions are produced in other 

 animals by muscles placed on opposite sides of the 

 body, but it would never do for birds to have a heavy 

 ma.ss of flesh on their backs. Accordingly, by a special 

 and most simple contrivance, both movements are brought 

 about by muscles conveniently placed in layers on the 

 under surface of the body. The muscles which pull 

 down the wing act directly on the wing bones, but the 

 muscles which pull them up, act indirectly : the sort of 

 cord in which they end being bent round a bony pulley so 

 as completely to reverse the action they would otherwise 

 produce. This is the reason why there is so much meat 

 on the breast of a bird — such as a partridge or a wood- 

 cock. It consists of the muscles which both pull down the 

 wings and raise them. The relation which exists between 

 the volume of these muscles and the power of flight is 

 well instanced by the difference in the quantity of meat 

 we find on the breast of a wild duck and a tame duck 

 respectively. 



A bird might, however, have the most voluminous of 

 muscles, but they would be of small use to it, were they 

 not stimulated by a copious supply of vivifying blood, 

 kept pure by a most efficient process of respiration. And 

 these aids are supplied with very exceptional complete- 

 ness. 



It is plain that in such a creature as a bird, the further 

 any organ may be removed from the centre of gravity, 

 the more necessary it becomes that it should be neither 

 heavy nor bulky. Thus a bird's arm and hand are 

 reduced to what is just necessary to sustain and w^eld 

 the large feathers which form the wing. The hand is 

 especially diminished, and its few rudimentary fingers are 

 closely bound together in a fold of skin. And yet birds 

 have a great many "handy " actions to perform. What 



